Glycolic acid copolymer and method for production thereof

ABSTRACT

A glycolic acid copolymer comprising (a) 80 to less than 95% by mole of glycolic acid monomer units, (b) 5.0 to 20.0% by mole of non-glycolic, hydroxycarboxylic acid monomer units, and (c) 0 to 0.10% by mole of diglycolic acid monomer units, the non-glycolic, hydroxycarboxylic acid monomer units (b) constituting a plurality of segments each independently consisting of at least one monomer unit (b), wherein the segments have an average chain length of from 1.00 to 1.50 in terms of the average number of monomer unit or units (b), the total of the components (a), (b) and (c) being 100% by mole, the glycolic acid copolymer having a weight average molecular weight of 50,000 or more.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a glycolic acid copolymer. Moreparticularly, the present invention is concerned with a glycolic acidcopolymer comprising (a) glycolic acid monomer units as a maincomponent, (b) non-glycolic, hydroxycarboxylic acid monomer units, andoptionally (c) diglycolic acid monomer units in not more than a specificamount, the non-glycolic, hydroxycarboxylic acid monomer units (b)constituting a plurality of segments each independently consisting of atleast one non-glycolic, hydroxycarboxylic acid monomer unit (b), whereinthe segments have an average chain length of from 1.00 to 1.50 in termsof the average number of non-glycolic, hydroxycarboxylic acid monomerunit or units (b), wherein the glycolic acid copolymer has a weightaverage molecular weight of 50,000 or more. The glycolic acid copolymerof the present invention is a high quality, high molecular weightproduct which is advantageous not only in that the copolymer enablesproduction of a shaped article exhibiting excellent gas barrierproperty, satisfactory mechanical strength and satisfactorybiodegradability, but also in that the copolymer exhibits high heatstability, thereby greatly suppressing the occurrence of discolorationeven when melt-shaped at high temperatures. The present invention isalso concerned with a method for producing the above-mentioned glycolicacid copolymer efficiently and stably.

2. Prior Art

In recent years, the problem of plastic materials wastes have beenattracting attention from the viewpoint of environmental protection. Forfacilitating environmental protection, there is an increasing demand forpolymers which can be spontaneously degraded in natural environment andfor shaped articles produced from such polymers. A polyglycolic acid anda glycolic acid copolymer have not only a good balance of heatresistance, mechanical strength and biodegradability, but also extremelyexcellent, gas barrier property. By virtue of such excellent properties,polyglycolic acids and glycolic acid copolymers are attracting attentionas biodegradable polymeric materials which are suitable for producingpackaging materials, such as containers and films. Therefore, in theart, studies have been being conducted for developing a high molecularweight polyglycolic acid and a high molecular weight glycolic acidcopolymer which have a satisfactory mechanical strength required ofshaped articles.

However, a polyglycolic acid and a glycolic acid copolymer having a highglycolic acid monomer unit content have high melting temperatures and,hence, these polymers have defects not only in that a high temperatureis necessary for melt shaping these polymers, but also in that thedifference between the melting temperature and the decompositiontemperature is small. Therefore, problems due to poor heat stabilityhave been encountered in that these polymers exhibit markeddiscoloration at the time of melt shaping, that these polymers have poorresistance to heat aging, and that these polymers generate heatdecomposition products when heated.

In an attempt to solve such problems, methods using a phosphoruscompound as a discoloration inhibitor have been proposed. However, thesemethods have not enabled production of a polyglycolic acid and aglycolic acid copolymer which have satisfactory heat stability.

For improving the heat stability of a polyglycolic acid and a glycolicacid copolymer (hereinafter, these polymers are frequently, collectivelyreferred to as “glycolic acid polymer”), a method has been proposed inwhich the terminal functional groups of a glycolic acid polymer arereacted with a specific compound (see, for example, Unexamined JapanesePatent Application Laid-Open Specification No. 56-157422). This methodis effective for suppressing the depolymerization of a glycolic acidpolymer at the time of shaping. However, this method does not exhibit asatisfactory effect of suppressing the discoloration at the time ofshaping.

For solving the problem of the poor heat stability of a polymer, thereis a generally employed measure in which copolymerization is performedfor producing a copolymer having a lowered melting temperature. Thismeasure has also been employed with respect to a glycolic acid polymer,and studies have been performed for producing various glycolic acidcopolymers having a lowered melting temperature.

For example, there has been proposed a method for producing a glycolicacid copolymer having a high molecular weight, in which many steps areperformed, as follows: glycolic acid and/or a derivative thereof issubjected to dehydration condensation to obtain a dehydrationcondensation product; the obtained dehydration condensation product issubjected to thermal decomposition to produce a cyclic dimeric glycolate(so-called “glycolide”); the obtained glycolide is purified to a highdegree; and the resultant highly purified glycolide is subjected toring-opening polymerization with, e.g., cyclic dimeric lactate(so-called “lactide”) in the presence of a catalyst, thereby obtaining aglycolic acid copolymer (see, for example, Unexamined Japanese PatentApplication Laid-Open Specification No. 48-62899 (corresponding to U.S.Pat. No. 3,839,297 and GB1416196 A)).

However, a glycolic acid copolymer (such as a glycolide-lactidecopolymer) obtained by the above-mentioned method using a ring-openingpolymerization is likely to have a structure in which comonomer units(e.g., lactic acid monomer units in the above-mentionedglycolide-lactide copolymer) are introduced as polymer blocks into theprimary structure of the polymer. Therefore, when the amount of thecomonomer units is small, a satisfactory effect of lowering the meltingtemperature of a polymer cannot be obtained and, hence, the effect ofsuppressing the discoloration at the time of shaping becomesunsatisfactory.

On the other hand, when the amount of comonomer units (such as lacticacid monomer units) is increased for lowering the melting temperature ofa glycolic acid copolymer, the gas barrier property, which ischaracteristic of a glycolic acid copolymer, tends to become poor.

As another method for producing a glycolic acid copolymer by using aring-opening polymerization, a method has been proposed in whichglycolide is copolymerized with, e.g., ε-caprolactone, trimethylenecarbonate, p-dioxanone or a copolymer compound, such as a cyclic dimericester of glycolic acid with a malate (see Unexamined Japanese PatentApplication Laid-Open Specification No. 3-269013 (corresponding toDE3335588 A, GB2127839 A and U.S. Pat. No. 4,605,730), Examined JapanesePatent Application Publication No. 63-47731 (corresponding to GB2033411A, DE2850824 A and U.S. Pat. No. 4,243,775), Unexamined Japanese PatentApplication Laid-Open Specification No. 9-12689 (corresponding toEP751165 A2 and U.S. Pat. No. 5,633,343) and Unexamined Japanese PatentApplication Laid-Open Specification No. 2-209918).

On the other hand, as another method for producing a glycolic acidcopolymer, there is known a method in which, for example, mainlyglycolic acid and/or a derivative thereof is polycondensed with acomonomer. The method using a polycondensation is commercially moreadvantageous than the method using a ring-opening polymerization, inthat the former involves fewer steps than the latter. Further, themethod using a polycondensation is advantageous in that comonomer unitscan be randomly introduced into the primary structure of the resin.Therefore, the method using a polycondensation is highly effective forimproving the properties of a glycolic acid copolymer. For example, bythe method using a polycondensation, the melting temperature can begreatly lowered by introducing a small amount of comonomer units. Forthe reason of these advantages, the method using a polycondensation hasbeen considered as a promising polymerization method capable ofproducing a glycolic acid copolymer having satisfactory properties withrespect to shapability and gas barrier property, and various studieshave heretofore been made on the method using a polycondensation.Various glycolic acid copolymers produced by this method have beenproposed, as follows.

For example, Japanese Patent Application prior-to-examinationPublication (Tokuhyo) No. 7-501102 (corresponding to WO93/10169)discloses a copolymer obtained from glycolic acid and a polycarboxylicacid containing 2 or more carboxyl groups per molecule. However, thispatent document has no description about a high molecular weightcopolymer (for example, a copolymer having a weight average molecularweight of 50,000 or more). In Unexamined Japanese Patent ApplicationLaid-Open Specification No. 11-255873, a copolymer is proposed which iscomprised of hydroxycarboxylic acid monomer units, aliphaticdicarboxylic acid monomer units and ethylene oxide/propylene oxide blockcopolymer units and which has a weight average molecular weight of from50,000 to 1,000,000. Further, Unexamined Japanese Patent ApplicationLaid-Open Specification No. 8-3296 proposes an aliphatic polyestercopolymer which is comprised of aliphatic hydroxycarboxylic acid monomerunits, aliphatic diol monomer units and aliphatic dicarboxylic acidmonomer units and which has a number average molecular weight of from10,000 to 100,000. In these patent documents, copolymers containinglactic acid monomer units as hydroxycarboxylic acid monomer units areexemplified, and working examples are described in which such acopolymer is shaped into a fiber, sheet or the like. However, thecopolymers exemplified in these patent documents have a problem in that,when a copolymer contains a large amount of glycolic acid monomer units,the heat stability of the copolymer is not satisfactory and, hence, amarked discoloration is likely to occur at the time of melt shaping.

There has also been proposed an aliphatic polyester which is comprisedof glycol monomer units and at least one member selected from the groupconsisting of glycolic acid monomer units and lactic acid monomer unitsand which has a solution viscosity of 0.35 or more (see, for example,Unexamined Japanese Patent Application Laid-Open Specification No.1-156319). However, such copolymer has low heat stability and exhibitsmarked discoloration at the time of melt shaping.

Further, there has been proposed a copolymer which is obtained by atransesterification reaction between (A) a polyglycolic acid or acopolymer of glycolide and lactide and (B) a polyester comprised ofdiglycolic acid monomer units and diol compound monomer units, whereinpolyester (B) is used in an amount of from 2 to 50% by weight, based onthe total weight of raw material (A) and polyester (B) (see, forexample, Unexamined Japanese Patent Application Laid-Open SpecificationNo. 52-147691 (corresponding to GB1572362, U.S. Pat. No. 4,048,256, U.S.Pat. No. 4,095,600, U.S. Pat. No. 4,118,470 and U.S. Pat. No.4,122,129)). However, the heat stability of the copolymer is notsatisfactory, and a marked discoloration is likely to occur especiallyat the time of melt shaping.

Unexamined Japanese Patent Application Laid-Open Specification No.9-808220 (corresponding to WO97/08220) discloses a method for producinga polyhydroxycarboxylic acid which has a weight average molecular weightof 50,000 or more, in which a hydroxycarboxylic acid or an oligomerthereof is subjected to polycondensation in the presence of an inorganicsolid acid catalyst and an alkaline earth metallic compound catalyst.However, the polyhydroxycarboxylic acid obtained by this method isdiscolored to assume a pale brown color and, hence, has a poor quality.In addition, the heat stability of the polyhydroxycarboxylic acid islow, and the discoloration at the time of melt shaping is marked.

Unexamined Japanese Patent Application Laid-Open Specification No.11-130847 (corresponding to WO99/19378) discloses a method for producinga high molecular weight polyglycolic acid, in which a hydrolyzate ofmethyl glycolate is subjected to polycondensation to obtain a prepolymerand, then, the obtained prepolymer is subjected to solid phasepolymerization. However, the obtained polyglycolic acid exhibits poorheat stability and marked discoloration at the time of melt shaping.

As described hereinabove, there has been totally unknown a glycolic acidcopolymer containing a large amount of glycolic acid monomer units,which is advantageous not only in that it exhibits high heat stabilityat the time of melt shaping, but also in that it enables production of ashaped article exhibiting high mechanical strength and excellent gasbarrier property.

SUMMARY OF THE INVENTION

In this situation, the present inventors have made extensive andintensive studies with a view toward developing a high quality, highmolecular weight glycolic acid copolymer which is advantageous not onlyin that the copolymer enables production of a shaped article exhibitingexcellent gas barrier property and satisfactory mechanical strength aswell as biodegradability, but also in that the copolymer exhibits highheat stability, thereby greatly suppressing the occurrence ofdiscoloration even when melt-shaped at high temperatures. As a result,it has unexpectedly been found that, when a glycolic acid copolymer isproduced by polycondensation under melt conditions using glycolic acidand/or a derivative thereof as a raw material, diglycolic acid monomerunits are formed due to a diglycolic acid-forming, side reactionrepresented by the below-mentioned formula at the early stage of thepolycondensation, and that the content of the above-mentioned diglycolicacid monomer units in the copolymer is greatly varied depending on theproduction conditions.HO—CH₂—COOH+HO—CH₂—COOH →HOOC—CH₂—O—CH₂—COOH+H₂O

The present inventors have also made extensive and intensive studies onthe relationship between the primary structure of a glycolic acidcopolymer and the heat stability and gas barrier property of thecopolymer. As a result, it has surprisingly been found that theabove-mentioned problems of the prior art can be solved by a glycolicacid copolymer comprising glycolic acid monomer units as a maincomponent, non-glycolic, hydroxycarboxylic acid monomer units in aspecific amount, and optionally diglycolic acid monomer units, whereinthe content of the optional diglycolic acid monomer units is reduced tonot more than a specific value, wherein the glycolic acid copolymer hasa weight average molecular weight of 50,000 or more. It has also beenfound that such high molecular weight glycolic acid copolymer havingexcellent properties can be efficiently and stably obtained by a methodin which a raw material mixture which comprises a starting materialcomprised of glycolic acid and/or a derivative thereof and a reactantcomprised of a non-glycolic, hydroxycarboxylic acid and/or a derivativethereof, the reactant being copolymerizable with the starting material,is provided and subjected to a preliminary polycondensation reaction ata specific reaction temperature, thereby obtaining a reaction mixturecontaining a glycolic acid copolymer prepolymer, and then thetemperature of the obtained reaction mixture is elevated to a specificvalue under specific temperature elevation conditions, followed by afinal polycondensation reaction. Based on these findings, the presentinvention has been completed.

Accordingly, it is a primary object of the present invention to providea high quality, high molecular weight glycolic acid copolymer which isadvantageous not only in that the copolymer enables production of ashaped article exhibiting excellent gas barrier property andsatisfactory mechanical strength as well as biodegradability, but alsoin that the copolymer exhibits high heat stability, thereby greatlysuppressing the occurrence of discoloration even when melt-shaped athigh temperatures.

It is another primary object of the present invention is to provide amethod for producing the above-mentioned excellent glycolic acidcopolymer, efficiently and stably.

The foregoing and other objects, features and advantages of the presentinvention will be apparent from the following detailed description andappended claims.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect of the present invention, there is provided a glycolicacid copolymer comprising:

-   -   (a) 80 to less than 95% by mole of glycolic acid monomer units,    -   (b) 5.0 to 20.0% by mole of non-glycolic, hydroxycarboxylic acid        monomer units, and    -   (c) 0 to 0.10% by mole of diglycolic acid monomer units, the        non-glycolic, hydroxycarboxylic acid monomer units (b)        constituting a plurality of segments each independently        consisting of at least one non-glycolic, hydroxycarboxylic acid        monomer unit (b), wherein the segments have an average chain        length of from 1.00 to 1.50 in terms of the average number of        non-glycolic, hydroxycarboxylic acid monomer unit or units (b),        the total of the components (a), (b) and (c) being 100% by mole,        the glycolic acid copolymer having a weight average molecular        weight of 50,000 or more.

For easy understanding of the present invention, the essential featuresand various preferred embodiments of the present invention areenumerated below.

1. A glycolic acid copolymer comprising:

-   -   (a) 80 to less than 95% by mole of glycolic acid monomer units,    -   (b) 5.0 to 20.0% by mole of non-glycolic, hydroxycarboxylic acid        monomer units, and    -   (c) 0 to 0.10% by mole of diglycolic acid monomer units, the        non-glycolic, hydroxycarboxylic acid monomer units (b)        constituting a plurality of segments each independently        consisting of at least one non-glycolic, hydroxycarboxylic acid        monomer unit (b), wherein the segments have an average chain        length of from 1.00 to 1.50 in terms of the average number of        non-glycolic, hydroxycarboxylic acid monomer unit or units (b),    -   the total of the components (a), (b) and (c) being 100% by mole,    -   the glycolic acid copolymer having a weight average molecular        weight of 50,000 or more.

2. The glycolic acid copolymer according to item 1 above, wherein theweight average molecular weight of the glycolic acid copolymer is 80,000or more.

3. The glycolic acid copolymer according to item 1 or 2 above, whereinthe amount of diglycolic acid monomer units (c) is from more than 0 to0.09% by mole, based on the total molar amount of components (a), (b)and (c).

4. The glycolic acid copolymer according to any one of items 1 to 3above, wherein the weight average molecular weight of the glycolic acidcopolymer is 100,000 or more.

5. The glycolic acid copolymer according to any one of items 1 to 4above, wherein the average chain length of the segments eachindependently consisting of at least one non-glycolic, hydroxycarboxylicacid monomer unit (b) is from 1.00 to 1.20.

6. The glycolic acid copolymer according to any one of items 1 to 5above, wherein the non-glycolic, hydroxycarboxylic acid monomer units(b) are non-glycolic, monohydroxymonocarboxylic acid monomer units.

7. The glycolic acid copolymer according to any one of items 1 to 6above, which further comprises a polyol monomer unit (d).

8. The glycolic acid copolymer according to item 7 above, wherein thepolyol monomer unit (d) comprises at least one member selected from thegroup consisting of monomer units derived from a diol having 3 or morecarbon atoms and monomer units derived from a compound having 4 or morecarbon atoms and 3 or more hydroxyl groups in the molecule.

9. The glycolic acid copolymer according to item 8 above, wherein thepolyol monomer unit (d) comprises a monomer unit derived from a polyolhaving 5 or more carbon atoms and 2 or 3 hydroxyl groups in themolecule.

10. The glycolic acid copolymer according to item 9 above, wherein thepolyol monomer units (d) are neopentyl glycol monomer units.

11. The glycolic acid copolymer according to any one of items 7 to 10above, which further comprises a polycarboxylic acid monomer unit (e)other than diglycolic acid monomer units, wherein the total amount ofthe polyol monomer units (d), the polycarboxylic acid monomer units (e),and the diglycolic acid monomer units (c) is less than 2.0% by mole,based on the total molar amount of components (a), (b), (c), (d) and(e).

12. The glycolic acid copolymer according to item 11 above, wherein thetotal amount of the polyol monomer units (d), the polycarboxylic acidmonomer units (e), and the diglycolic acid monomer units (c) is frommore than 0.02 to less than 2.0% by mole, based on the total molaramount of components (a), (b), (c), (d) and (e), and the amount of thepolyol monomer units (d) is from 0.02 to less than 2.0% by mole, basedon the total molar amount of components (a), (b), (c), (d) and (e).

13. The glycolic acid copolymer according to any one of items 1 to 12above, wherein the non-glycolic, hydroxycarboxylic acid monomer units(b) comprise at least one member selected from the group consisting oflactic acid monomer units and 6-hydroxyhexanoic acid monomer units.

14. The glycolic acid copolymer according to any one of items 1 to 13above, which is obtained by polycondensing at least one startingmaterial selected from the group consisting of glycolic acid and aderivative thereof with a reactant copolymerizable with the at least onestarting material, wherein the reactant comprises at least one memberselected from the group consisting of a non-glycolic, hydroxycarboxylicacid and a derivative thereof.

15. A method for producing a glycolic acid copolymer, which comprisesthe steps of:

(A) providing a raw material mixture comprising at least one startingmaterial selected from the group consisting of glycolic acid and aderivative thereof, and a reactant copolymerizable with the at least onestarting material, wherein the reactant comprises at least one memberselected from the group consisting of a non-glycolic, hydroxycarboxylicacid, a derivative thereof and optionally at least one compound selectedfrom the group consisting of a polyol, a polycarboxylic acid and aderivative of the polycarboxylic acid, and subjecting the raw materialmixture to a preliminary polycondensation reaction at a temperature inthe range of from 20 to 160° C., thereby obtaining a reaction mixturecontaining a glycolic acid copolymer prepolymer having a weight averagemolecular weight of from 700 to 5,000,

(B) elevating the temperature of the reaction mixture to 190° C. withina period of 100 minutes as measured from the start of the temperatureelevation in step (B), and

(C) performing a heat treatment of the reaction mixture at a temperaturein the range of from 190 to 300° C. to effect a final polycondensationreaction, wherein the final polycondensation reaction is performed so asto obtain a glycolic acid copolymer having a weight average molecularweight of 10,000 or more, wherein the final polycondensation reaction isperformed under conditions wherein the increasing rate of weight averagemolecular weight of the glycolic acid copolymer being produced ismaintained at 1,000 per hour or more until the weight average molecularweight reaches at least 10,000.

16. The method according to item 15 above, wherein the heat treatmentfor effecting the final polycondensation reaction is performed so as toobtain the glycolic acid copolymer of any one of items 1 to 14 above,which has a weight average molecular weight of 50,000 or more.

17. The method according to item 15 above, wherein the raw materialmixture satisfies the following formulae (1) to (3):0.8≦X¹≦0.95  (1),0.05≦X²  (2), andX¹ +X ² +X ₃ +X ⁴=1  (3)wherein:

-   X¹ represents the calculated molar ratio of the at least one    starting material selected from the group consisting of glycolic    acid and a derivative thereof,-   X² represents the calculated molar ratio of the at least one member    selected from the group consisting of a non-glycolic,    hydroxycarboxylic acid and a derivative thereof,-   X³ represents the calculated molar ratio of an optional polyol,-   X⁴ represents the calculated molar ratio of at least one optional    raw material selected from the group consisting of a polycarboxylic    acid and a derivative thereof,    -   the calculated molar ratio of each raw material being defined as        the ratio of the molar amount of the unit structure obtained by        hydrolysis of each raw material to the total molar amount of the        unit structures of all raw materials, and    -   each of X³ and X⁴ is independently 0 or more.

18. The method according to item 17 above, wherein the raw materialmixture satisfies the following formulae (4) and (5): $\begin{matrix}{{\frac{X^{4}}{X^{1} + X^{2}} \leq 0.001},{and}} & (4) \\{{0 < \frac{X^{3}}{X^{1} + X^{2}} \leq 0.01},} & (5)\end{matrix}$

-   -   wherein X¹ to X⁴ are as defined for formulae (1) to (3) above,        provided that X³ is more than 0, and X⁴ is 0 or more.

19. The method according to item 17 above, wherein the raw materialmixture satisfies the following formulae (6) and (7): $\begin{matrix}{{0.001 < \frac{X^{4}}{X^{1} + X^{2}} \leq 0.088},{and}} & (6) \\{{1 \leq \frac{X^{3}}{X^{4}} \leq 2},} & (7)\end{matrix}$

-   -   wherein X¹ to X⁴ are as defined for formulae (1) to (3) above,        provided that each of X³ and X⁴ is more than 0.

20. The method according to item 17 above, wherein the raw materialmixture satisfies the following formula (8): $\begin{matrix}{{0.0002 \leq \frac{X^{3} + X^{4}}{X^{1} + X^{2} + X^{3} + X^{4}} < 0.02},} & (8)\end{matrix}$

-   -   wherein X¹ to X⁴ are as defined for formulae (1) to (3) above,        provided that X³ is more than 0, and X⁴ is 0 or more.

21. A method for producing a glycolic acid copolymer of any one of items1 to 14 above, which comprises the steps of:

-   -   crystallizing the glycolic acid copolymer obtained by the method        of item 15 above, thereby obtaining a crystallized glycolic acid        copolymer, and    -   subjecting the obtained crystallized glycolic acid copolymer to        a solid phase polymerization, thereby increasing the degree of        polymerization of the crystallized glycolic acid copolymer.

22. The method according to item 21 above, wherein the crystallizedglycolic acid copolymer before the solid phase polymerization has aweight average molecular weight of 25,000 or more, as measured by gelpermeation chromatography using, as an eluent, an 80 mM sodiumtrifluoroacetate solution in hexafluoroisopropanol and using acalibration curve obtained with respect to standard monodispersepolymethyl methacrylate samples.

23. A shaped article obtained from the glycolic acid copolymer of anyone of items 1 to 14 above.

The glycolic acid copolymer of the present invention exhibits high heatstability at the time of melt shaping, thereby greatly suppressing theoccurrence of discoloration even when melt-shaped at high temperatures,so that the quality of the glycolic acid copolymer can be maintained ata high level. Further, a shaped article obtained by melt shaping theglycolic acid copolymer of the present invention has excellent gasbarrier property and satisfactory mechanical strength as well asbiodegradability. Therefore, the glycolic acid copolymer of the presentinvention is suitable for use as a raw material for producing packagingmaterials, such as containers and films.

The weight average molecular weight of the glycolic acid copolymer ofthe present invention is 50,000 or more, preferably 80,000 or more, morepreferably 100,000 or more. When the weight average molecular weight isless than 50,000, the glycolic acid copolymer does not have satisfactorymechanical strength required of shaped articles, such as containers andfilms. With respect to the weight average molecular weight, there is noparticular upper limit. However, from the viewpoint of achieving asuitable fluidity at the time of shaping, the weight average molecularweight of the glycolic acid copolymer is preferably 1,000,000 or less,more preferably 700,000 or less, still more preferably 500,000 or less.

In the present invention, the weight average molecular weight (Mw) ofthe glycolic acid copolymer is a value as measured by gel permeationchromatography (GPC) using, as an eluent, an 80 mM sodiumtrifluoroacetate solution in hexafluoroisopropanol. More specifically,first, a calibration curve is obtained by a method in which monodispersepolymethyl methacrylate samples having known molecular weights andmethyl methacrylate monomer are used as reference standards, and theelution time is detected by RI. The weight average molecular weight (Mw)is calculated using the calibration curve and the elution time of theglycolic acid copolymer.

Generally, the molecular weight of a polymer is measured by GPC as aweight average molecular weight or a number average molecular weight. Inthis connection, it should be noted that, when the molecular weight of apolyglycolic acid or a glycolic acid copolymer containing about 80% bymole or more of glycolic acid monomer units is measured by a method inwhich hexafluoroisopropanol (which can dissolve the polyglycolic acid orglycolic acid copolymer) is used as an eluent, and monodispersepolymethyl methacrylate and optionally methyl methacrylate monomer areused as reference standards, the weight average value obtainedconsiderably varies depending on the absence or presence of sodiumtrifluoroacetate in the eluent and on the content of optional sodiumtrifluoroacetate in the eluent. Specifically, in the case where GPC isperformed using an eluant which does not contain sodium trifluoroacetateor which contains only a small amount of sodium trifluoroacetate, themolecular weight value measured would be considerably large or would beirreproducible. Therefore, in the present invention, as mentioned above,a weight average molecular weight is defined as a value determined byGPC using, as an eluent, an 80 mM sodium trifluoroacetate inhexafluoroisopropanol.

The glycolic acid copolymer of the present invention comprises:

-   -   (a) 80 to less than 95% by mole of glycolic acid monomer units,    -   (b) 5.0 to 20.0% by mole of non-glycolic, hydroxycarboxylic acid        monomer units, and    -   (c) 0 to 0.10% by mole of diglycolic acid monomer units,    -   the total of the components (a), (b) and (c) being 100% by mole.

As mentioned above, the amount of glycolic acid monomer units (a)contained in the glycolic acid copolymer of the present invention is 80to less than 95% by mole. The amount of glycolic acid monomer units (a)is preferably 82 to less than 95% by mole, more preferably 83 to 94% bymole, most preferably 85 to 93% by mole. When the amount of glycolicacid monomer units (a) is less than 80% by mole, the gas barrierproperty of the copolymer is unsatisfactory, and a shaped articleproduced by melt shaping the glycolic acid copolymer has unsatisfactoryproperties with respect to mechanical properties, such as strength andelasticity. On the other hand, when the amount of glycolic acid monomerunits (a) is 95% by mole or more, the heat stability of the glycolicacid copolymer is markedly lowered and, hence, discoloration at the timeof melt shaping becomes marked.

As mentioned above, the glycolic acid copolymer of the present inventioncontains 5.0 to 20.0% by mole of non-glycolic, hydroxycarboxylic acidmonomer units (b). Further, non-glycolic, hydroxycarboxylic acid monomerunits (b) constitute a plurality of segments each independentlyconsisting of at least one non-glycolic, hydroxycarboxylic acid monomerunit (b), wherein the segments have an average chain length of from 1.00to 1.50, preferably 1.00 to 1.20, more preferably 1.00 to 1.10, stillmore preferably 1.00 to 1.07, most preferably 1.00 to 1.05 in terms ofthe average number of non-glycolic, hydroxycarboxylic acid monomer unitor units (b).

When the amount of non-glycolic, hydroxycarboxylic acid monomer units(b) is less than 5.0% by mole, the heat stability of the copolymer islowered and, hence, discoloration at the time of melt shaping becomesmarked.

When the average chain length of non-glycolic, hydroxycarboxylic acidmonomer units (b) is more than 1.50, non-glycolic, hydroxycarboxylicacid monomer units (b) are introduced as polymer blocks into thecopolymer. Therefore, in such case, the effect of lowering the meltingtemperature of the glycolic acid copolymer by copolymerization cannot besatisfactory exhibited, so that the shapability and gas barrier propertyof the glycolic acid copolymer are lowered. The minimum of the averagechain length is usually 1.00.

In the present invention, the average chain length of non-glycolic,hydroxycarboxylic acid monomer units (b) is a value of the average chainlength (γ) of non-glycolic, hydroxycarboxylic acid monomer units (b),which is calculated from an integrated value determined from the ¹³C-NMRspectral pattern of a carbonyl group, the ¹³C-NMR being performed usinghexafluoroisopropanol as a solvent under conditions wherein protons arecompletely decoupled by eliminating the nuclear Overhauser effect.Specifically, the average chain length (γ) of a plurality of segments,each constituted by the non-glycolic, hydroxycarboxylic acid monomerunit(s), is calculated using the following values: an integratedintensity (α) of a peak ascribed to a carbonyl group formed between twoadjacent non-glycolic, hydroxycarboxylic acid monomer units (b); and sum(β) of an integrated intensity of a peak ascribed to a carbonyl groupformed between a non-glycolic, hydroxycarboxylic acid monomer unit (b)and a glycolic acid monomer unit (a) which are adjacent to each otherand an integrated intensity of a peak ascribed to a carbonyl groupformed between a non-glycolic, hydroxycarboxylic acid monomer unit (b)and a monomer unit other than a non-glycolic, hydroxycarboxylic-acidmonomer unit (b) which are adjacent to each other. Specifically, theaverage chain length (y) is calculated by the following formula:γ=α/β+1

When two or more types of non-glycolic, hydroxycarboxylic acid monomerunits (b) are contained in the copolymer, a segment consisting of twonon-glycolic, hydroxycarboxylic acid monomer units (b) may beconstituted by two different types of non-glycolic, hydroxycarboxylicacid monomer units (b).

As non-glycolic, hydroxycarboxylic acid monomer units (b) copolymerizedin the glycolic acid copolymer, there can be used at least one memberselected from the group consisting of aliphaticmonohydroxymonocarboxylic acid monomer units having 3 or more carbonatoms, aliphatic polyhydroxymonocarboxylic acid monomer units, aliphaticmonohydroxypolycarboxylic acid monomer units, aliphaticpolyhydroxypolycarboxylic acid monomer units, aromaticmonohydroxymonocarboxylic acid monomer units, aromaticpolyhydroxymonocarboxylic acid monomer units, aromaticmonohydroxypolycarboxylic acid monomer units, aromaticpolyhydroxypolycarboxylic acid monomer units and hydroxycarboxylic acidmonomer units containing a hetero atom. Specific examples of aliphaticmonohydroxymonocarboxylic acid monomer units having 3 or more carbonatoms include lactic acid monomer unit, 2-hydroxybutanoic acid monomerunit, 2-hydroxypentanoic acid monomer unit, 2-hydroxyhexanoic acidmonomer unit, 2-hydroxyheptanoic acid monomer unit, 2-hydroxyoctanoicacid monomer unit, 2-hydroxy-2-methylpropanoic acid monomer unit,2-hydroxy-2-methylbutanoic acid monomer unit, 2-hydroxy-2-ethylbutanoicacid monomer unit, 2-hydroxy-2-methylpentanoic acid monomer unit,2-hydroxy-2-ethylpentanoic acid monomer unit,2-hydroxy-2-propylpentanoic acid monomer unit,2-hydroxy-2-butylpentanoic acid monomer unit, 2-hydroxy-2-methylhexanoicacid monomer unit, 2-hydroxy-2-ethylhexanoic acid monomer unit,2-hydroxy-2-propylhexanoic acid monomer unit, 2-hydroxy-2-butylhexanoicacid monomer unit, 2-hydroxy-2-pentylhexanoic acid monomer unit,2-hydroxy-2-methylheptanoic acid monomer unit,2-hydroxy-2-ethylheptanoic acid monomer unit,2-hydroxy-2-propylheptanoic acid monomer unit,2-hydroxy-2-butylheptanoic acid monomer unit,2-hydroxy-2-pentylheptanoic acid monomer unit,2-hydroxy-2-hexylheptanoic acid monomer unit, 2-hydroxy-2-methyloctanoicacid monomer unit, 2-hydroxy-2-ethyloctanoic acid monomer unit,2-hydroxy-2-propyloctanoic acid monomer unit, 2-hydroxy-2-butyloctanoicacid monomer unit, 2-hydroxy-2-pentyloctanoic acid monomer unit,2-hydroxy-2-hexyloctanoic acid monomer unit, 2-hydroxy-2-heptyloctanoicacid monomer unit, 3-hydroxypropanoic acid monomer unit,3-hydroxybutanoic acid monomer unit, 3-hydroxypentanoic acid monomerunit, 3-hydroxyhexanoic acid monomer unit, 3-hydroxyheptanoic acidmonomer unit, 3-hydroxyoctanoic acid monomer unit,3-hydroxy-3-methylbutanoic acid monomer unit,3-hydroxy-3-methylpentanoic acid monomer unit,3-hydroxy-3-ethylpentanoic acid monomer unit, 3-hydroxy-3-methylhexanoicacid monomer unit, 3-hydroxy-3-ethylhexanoic acid monomer unit,3-hydroxy-3-propylhexanoic acid monomer unit,3-hydroxy-3-methylheptanoic acid monomer unit,3-hydroxy-3-ethylheptanoic acid monomer unit,3-hydroxy-3-propylheptanoic acid monomer unit,3-hydroxy-3-butylheptanoic acid monomer unit, 3-hydroxy-3-methyloctanoicacid monomer unit, 3-hydroxy-3-ethyloctanoic acid monomer unit,3-hydroxy-3-propyloctanoic acid monomer unit, 3-hydroxy-3-butyloctanoicacid monomer unit, 3-hydroxy-3-pentyloctanoic acid monomer unit,4-hydroxybutanoic acid monomer unit, 4-hydroxypentanoic acid monomerunit, 4-hydroxyhexanoic acid monomer unit, 4-hydroxyheptanoic acidmonomer unit, 4-hydroxyoctanoic acid monomer unit,4-hydroxy-4-methylpentanoic acid monomer unit,4-hydroxy-4-methylhexanoic acid monomer unit, 4-hydroxy-4-ethylhexanoicacid monomer unit, 4-hydroxy-4-methylheptanoic acid monomer unit,4-hydroxy-4-ethylheptanoic acid monomer unit,4-hydroxy-4-propylheptanoic acid monomer unit,4-hydroxy-4-methyloctanoic acid monomer unit, 4-hydroxy-4-ethyloctanoicacid monomer unit, 4-hydroxy-4-propyloctanoic acid monomer unit,4-hydroxy-4-butyloctanoic acid monomer unit, 5-hydroxypentanoic acidmonomer unit, 5-hydroxyhexanoic acid monomer unit, 5-hydroxyheptanoicacid monomer unit, 5-hydroxyoctanoic acid monomer unit,5-hydroxy-5-methylhexanoic acid monomer unit,5-hydroxy-5-methylheptanoic acid monomer unit,5-hydroxy-5-ethylheptanoic acid monomer unit, 5-hydroxy-5-methyloctanoicacid monomer unit, 5-hydroxy-5-ethyloctanoic acid monomer unit,5-hydroxy-5-propyloctanoic acid monomer unit, 6-hydroxyhexanoic acidmonomer unit, 6-hydroxyheptanoic acid monomer unit, 6-hydroxyoctanoicacid monomer unit, 6-hydroxy-6-methylheptanoic acid monomer unit,6-hydroxy-6-methyloctanoic acid monomer unit, 6-hydroxy-6-ethyloctanoicacid monomer unit, 7-hydroxyheptanoic acid monomer unit,7-hydroxyoctanoic acid monomer unit, 7-hydroxy-7-methyloctanoic acidmonomer unit, 8-hydroxyoctanoic acid monomer unit, 12-hydroxystearicacid monomer unit and 16-hydroxyhexadecanoic acid monomer unit. Specificexamples of aliphatic polyhydroxymonocarboxylic acid monomer unitsinclude glycelic acid monomer unit, arabinonic acid monomer unit,mannonic acid monomer unit and galactonic acid monomer unit. Specificexamples of aliphatic monohydroxypolycarboxylic acid monomer unitsinclude malic acid monomer unit and citric acid monomer unit. Specificexamples of aliphatic polyhydroxypolycarboxylic acid monomer unitsinclude diglycelic acid monomer unit and mannonic acid monomer unit.Specific examples of aromatic monohydroxymonocarboxylic acid monomerunits include hydroxybenzoic acid monomer unit and the like. Specificexamples of aromatic polyhydroxymonocarboxylic acid monomer unitsinclude 2,3-dihydroxybenzoic acid monomer unit, 2,4-dihydroxybenzoicacid monomer unit, 2,5-dihydroxybenzoic acid monomer unit,2,6-dihydroxybenzoic acid monomer unit, 3,4-dihydroxybenzoic acidmonomer unit and 3,5-dihydroxybenzoic acid monomer unit. Specificexamples of aromatic monohydroxypolycarboxylic acid monomer unitsinclude 4-hydroxyisophtalic acid monomer unit and 5-hydroxyisophtalicacid monomer unit. Specific examples of aromaticpolyhydroxypolycarboxylic acid monomer units include2,5-dihydroxyterephtalic acid monomer unit and the like. Specificexamples of hydroxycarboxylic acid monomer units containing a heteroatom include 2-hydroxyethoxyacetic acid monomer unit and2-hydroxypropoxyacetic acid monomer unit. Among these, with respect tomonomer units containing an asymmetric carbon atom therein, monomerunits may be of any of D-form and L-form, or may be a mixture of D-formand L-form. Further, these monomer units can be used individually or incombination.

Among the above-mentioned monomer units, from the viewpoint ofsuppressing the increase in the water absorbability of the copolymer tothereby lower the hydrolysis rate of the copolymer or from the viewpointof excellent processability (such as extensibility) of the copolymer andhigh flexibility of the shaped articles, monohydroxymonocarboxylic acidmonomer units having 3 or more carbon atoms are preferred. Morepreferred are aliphatic monohydroxymonocarboxylic acid monomer unitshaving 3 or more carbon atoms, and still more preferred are lactic acidmonomer unit, 3-hydroxybutyric acid monomer unit, 4-hydroxybutyric acidmonomer unit, 3-hydroxyvaleric acid monomer unit, 6-hydroxyhexanoic acidmonomer unit, 12-hydroxystearic acid monomer unit and16-hydroxyhexadecanoic acid monomer units, and a mixture thereof. Amongthese, from the viewpoint of ease of obtainment, lactic acid monomerunit, 6-hydroxyhexanoic acid monomer unit and a mixture thereof areespecially preferred, most preferably lactic acid monomer unit.

The amount of diglycolic acid monomer units (c) contained in theglycolic acid copolymer of the present invention is 0.10% by mole orless, based on the total molar amount of the components (a), (b) and(c). The present inventors have found that the heat stability and heataging resistance of a glycolic acid copolymer at the time of shaping canbe improved by reducing the amount of diglycolic acid monomer unitsformed at the early stage of the polycondensation reaction for producingthe glycolic acid copolymer. However, it is difficult to completelyprevent the formation of the diglycolic acid monomer units and, hence,the amount of the diglycolic acid monomer units (c) in the glycolic acidcopolymer of the present invention is generally more than 0% by mole,based on the total molar amount of the components (a), (b) and (c). Whenthe amount of the diglycolic acid monomer units (c) is not more than0.10% by mole, based on the total molar amount of the components (a),(b) and (c), the glycolic acid copolymer exhibits excellent heatstability and excellent resistance to heat aging. The amount ofdiglycolic acid monomer units (c) is preferably in the range of frommore than 0 to 0.09% by mole, more preferably from 0.01 to 0.08% bymole, based on the total molar amount of the components (a), (b) and(c).

In the present invention, the amount of diglycolic acid monomer units(c) is determined by means of a high-performance liquid chromatography(HPLC) analysis apparatus under the following conditions.

Specifically, a mass of a glycolic acid copolymer is pulverized,followed by drying at 80° C. in a vacuum for 6 hours, thereby obtaininga dried resin. 5 g of the obtained dried resin is weighed and, then,hydrolyzed in 20 ml of an 8 N aqueous NaOH solution at room temperaturefor 48 hours. To the resultant hydrolysis product is added 12.5 ml of aconcentrated hydrochloric acid to thereby obtain an acidified aqueoussolution. The obtained acidified aqueous solution is used as a samplesolution. With respect to the sample solution, HPLC is performed using a0.75% by weight aqueous phosphoric acid solution as an eluent underconditions wherein the column temperature is 40° C. and the flow rate ofthe eluent is 1 ml/minute. In the HPLC, the sample solution is flowedthrough 2 columns (RSpak (tradename) KC-811, manufactured and sold byShowa Denko K.K., Japan) which are connected in series, and theabsorbance of a peak ascribed to diglycolic acid, which is detected by aUV detector (wavelength: 210 nm), is measured. The amount of diglycolicacid monomer units (c) present in a glycolic acid copolymer is expressedin terms of the molar amount (% by mole) of diglycolic acid monomerunits (c) contained in the weighed dried resin mentioned above, whereinthe molar amount is calculated from the amount of diglycolic acidmonomer units present in the weighed dried resin, using a calibrationcurve of diglycolic acid which has been separately prepared.

The glycolic acid copolymer of the present invention may furthercomprise, as a component other than glycolic acid monomer units (a),non-glycolic, hydroxycarboxylic acid monomer units (b) and diglycolicacid monomer units (c), at least one member selected from the groupconsisting of a polyol monomer unit (d) and a polycarboxylic acidmonomer unit (e) other than diglycolic acid monomer units, wherein theseoptional components are used in amounts which do not adversely affectthe properties of the present invention.

It is preferred that the polyol monomer unit (d) used in the glycolicacid copolymer of the present invention has 2 or more hydroxyl groupsand 2 to 20 carbon atoms in the molecule. The amount of the polyolmonomer units (d) is preferably from more than 0% by mole to 0.3% bymole, more preferably from 0.02 to 0.20% by mole, based on the totalmolar amount of components (a), (b), (c) and (d). Examples of polyolmonomer units (d) include aliphatic diol monomer units, such as ethyleneglycol monomer unit, 1,3-propanediol monomer unit, 1,2-propanediolmonomer unit, 1,4-butanediol monomer unit, 2,3-butanediol monomer unit,1,5-pentanediol monomer unit, 1,6-hexanediol monomer unit,1,7-heptanediol monomer unit, 1,8-octanediol monomer unit,1,9-nonanediol monomer unit, 1,10-decanediol monomer unit,1,12-dodecanediol monomer unit, 1,4-cyclohexanediol monomer unit,1,2-cyclohexanediol monomer unit, 1,3-cyclohexanediol monomer unit andneopentyl glycol monomer unit; aromatic diol monomer units, such asbisphenol A monomer unit, catechol monomer unit, resorcinol monomerunit, 1,2-benzenedimethanol monomer unit, 1,3-benzenedimethanol monomerunit and 1,4-benzenedimethanol monomer unit; diol monomer unitscontaining hetero atoms, such as diethylene glycol monomer unit,triethylene glycol monomer unit and tetraethylene glycol monomer unit;aliphatic triol monomer units, such as glycerol monomer unit,1,2,4-butanetriol monomer unit, trimethylol ethane monomer unit,trimethylol propane monomer unit and butane-1,2,3-triol monomer unit;aromatic triol monomer units, such as 1,2,4-benzenetriol monomer unitand 1,3,5-benzenetriol monomer unit; and saccharide monomer units, suchas starch monomer unit, glucose monomer unit, cellulose monomer unit,hemicellulose monomer unit, xylose monomer unit, arabinose monomer unit,mannose monomer unit, galactose monomer unit, xylitol monomer unit,arabinitol monomer unit, mannitol monomer unit, galactitol monomer unit,pentaerythritol monomer unit, chitin monomer unit, chitosan monomerunit, a dextrin monomer unit, a dextran monomer unit, carboxymethylcellulose monomer unit, amylopectin monomer unit and glycogen monomerunit. These polyol monomer units can be used individually or incombination. Among the above-mentioned compounds, when a compound has anasymmetric carbon atom and, hence, exists as optical isomers, any of theisomers may be used.

Of these polyol monomer units, from the viewpoint of improving the heatstability and heat aging resistance of the glycolic acid copolymer atthe time of melt shaping, preferred are monomer units formed from a diolhaving 3 or more carbon atoms, for example, aliphatic diol monomerunits, such as 1,3-propanediol monomer unit, 1,2-propanediol monomerunit, 1,4-butanediol monomer unit, 2,3-butanediol monomer unit,1,5-pentanediol monomer unit, 1,6-hexanediol monomer unit,1,7-heptanediol monomer unit, 1,8-octanediol monomer unit,1,9-nonanediol monomer unit, 1,10-decanediol monomer unit,1,12-dodecanediol monomer unit, 1,4-cyclohexanediol monomer unit,1,2-cyclohexanediol monomer unit, 1,3-cyclohexanediol monomer unit andneopentyl glycol monomer unit; and aromatic diol monomer units, such asbisphenol A monomer unit, catechol monomer unit, resorcinol monomerunit, 1,2-benzenedimethanol monomer unit, 1,3-benzenedimethanol monomerunit and 1,4-benzenedimethanol monomer unit.

Among the above-mentioned preferred polyol monomer units, from theviewpoint of obtaining advantages not only in that there can be obtainedan improvement in the heat stability and heat aging resistance of theglycolic acid copolymer at the time of melt shaping, but also in that ashaped article having high flexibility can be obtained from the glycolicacid copolymer, it is more preferred to use, as a polyol monomer unit(d), aliphatic diol monomer units, such as 1,3-propanediol monomer unit,1,2-propanediol monomer unit, 1,4-butanediol monomer unit,2,3-butanediol monomer unit, 1,5-pentanediol monomer unit,1,6-hexanediol monomer unit, 1,7-heptanediol monomer unit,1,8-octanediol monomer unit, 1,9-nonanediol monomer unit,1,10-decanediol monomer unit, 1,12-dodecanediol monomer unit,1,4-cyclohexanediol monomer unit, 1,2-cyclohexanediol monomer unit,1,3-cyclohexanediol monomer unit and neopentyl glycol monomer unit.

On the other hand, for imparting an improved melt tension to theglycolic acid copolymer of the present invention, monomer units derivedfrom a compound having 3 or more hydroxyl groups in the molecule areused as the polyol monomer unit (d). When using such monomer units asthe polyol monomer units (d) in the glycolic acid copolymer, forstabilizing the effect of improving the melt tension of the copolymer,it is more preferred to use monomer units derived from a compound having4 or more carbon atoms and 3 or more hydroxyl groups in the molecule,for example, aliphatic triol monomer units, such as 1,2,4-butanetriolmonomer unit, trimethylol ethane monomer unit, trimethylol propanemonomer unit and butane-1,2,3-triol monomer unit; aromatic triol monomerunits, such as 1,2,4-benzenetriol monomer unit and 1,3,5-benzenetriolmonomer unit; and saccharide monomer units, such as xylitol monomerunit, arabinitol monomer unit, mannitol monomer unit, galactitol monomerunit and pentaerythritol monomer unit.

Of these polyol monomer units (d), still more preferred are monomerunits derived from a polyol having 5 or more carbon atoms and 2 or 3hydroxyl groups in the molecule, for example, aliphatic diol monomerunits, such as 1,5-pentanediol monomer unit, 1,6-hexanediol monomerunit, 1,7-heptanediol monomer unit, 1,8-octanediol monomer unit,1,9-nonanediol monomer unit, 1,10-decanediol monomer unit,1,12-dodecanediol monomer unit, 1,4-cyclohexanediol monomer unit,1,2-cyclohexanediol monomer unit, 1,3-cyclohexanediol monomer unit andneopentyl glycol monomer unit; and aliphatic triol monomer units, suchas trimethylol ethane monomer unit and trimethylol propane monomer unit.

Of these polyol monomer units, especially preferred is neopentyl glycolmonomer unit.

As mentioned above, in addition to glycolic acid monomer units (a),non-glycolic, hydroxycarboxylic acid monomer units (b) and diglycolicacid monomer units (c), the glycolic acid copolymer of the presentinvention may further comprise a polycarboxylic acid monomer unit (e)other than diglycolic acid monomer units, wherein the amount ofcomponent (e) is chosen so as not to adversely affect the properties ofthe present invention.

It is preferred that the polycarboxylic acid monomer unit (e) used inthe glycolic acid copolymer of the present invention has 2 or morecarboxyl groups and 2 to 20 carbon atoms in the molecule. The amount ofpolycarboxylic acid monomer units (e) is preferably from more than 0% bymole to 0.10% by mole, more preferably from 0.01 to 0.05% by mole, basedon the total molar amount of components (a), (b), (c) and (e). Examplesof polycarboxylic acid monomer units (e) include aliphatic dicarboxylicacid monomer units, such as oxalic acid monomer unit, malonic acidmonomer unit, glutaric acid monomer unit, succinic acid monomer unit,adipic acid monomer unit, pimelic acid monomer unit, suberic acidmonomer unit, azelaic acid monomer unit, sebacic acid monomer unit,undecanedioic acid monomer unit, dodecanedioic acid monomer unit,fumaric acid monomer unit, maleic acid monomer unit and1,4-cyclohexanedicarboxylic acid monomer unit; aromatic dicarboxylicacid monomer units, such as phthalic acid monomer unit, isophthalic acidmonomer unit and terephthalic acid monomer unit; aliphatic tricarboxylicacid monomer units, such as propanetricarboxylic acid monomer unit,trimellitic acid monomer unit, pyromellitic acid monomer unit and1,3,6-hexanetricarboxylic acid monomer unit; aromatic tricarboxylic acidmonomer units, such as 1,2,3-benzenetricarboxylic acid monomer unit,1,2,4-benzenetricarboxylic acid monomer unit and1,3,5-benzenetricarboxylic acid monomer unit; and carboxylic acidmonomer units having 4 or more carboxyl groups in the molecule, such asethylenediaminetetraaccetic acid monomer unit. These polycarboxylic acidmonomer units can be used individually or in combination.

Of these polycarboxylic acid monomer units (e), preferred are aliphaticdicarboxylic acid monomer units, such as oxalic acid monomer unit,malonic acid monomer unit, glutaric acid monomer unit, succinic acidmonomer unit, adipic acid monomer unit, pimelic acid monomer unit,suberic acid monomer unit, azelaic acid monomer unit, sebacic acidmonomer unit, undecanedioic acid monomer unit, dodecanedioic acidmonomer unit and 1,4-cyclohexanedicarboxylic acid monomer unit; aromaticdicarboxylic acid monomer units, such as phthalic acid monomer unit,isophthalic acid monomer unit and terephthalic acid monomer unit;aliphatic tricarboxylic acid monomer units, such as propanetricarboxylicacid monomer unit, trimellitic acid monomer unit, pyromellitic acidmonomer unit and 1,3,6-hexanetricarboxylic acid monomer unit; aromatictricarboxylic acid monomer units, such as 1,2,3-benzenetricarboxylicacid monomer unit, 1,2,4-benzenetricarboxylic acid monomer unit and1,3,5-benzenetricarboxylic acid monomer unit.

Further, from the viewpoint of improving the flexibility of the shapedarticle obtained from the glycolic acid copolymer of the presentinvention, it is still more preferred to use aliphatic dicarboxylic acidmonomer units, such as oxalic acid monomer unit, malonic acid monomerunit, glutaric acid monomer unit, succinic acid monomer unit, adipicacid monomer unit, pimelic acid monomer unit, suberic acid monomer unit,azelaic acid monomer unit, sebacic acid monomer unit, undecanedioic acidmonomer unit, dodecanedioic acid monomer unit and1,4-cyclohexanedicarboxylic acid monomer unit; and aliphatictricarboxylic acid monomer units, such as propanetricarboxylic acidmonomer unit, trimellitic acid monomer unit, pyromellitic acid monomerunit and 1,3,6-hexanetricarboxylic acid monomer unit.

In the present invention, the glycolic acid copolymer may furthercomprise a monomer unit other than the monomer units mentioned above, aslong as the presence of such a further optional monomer unit does notadversely affect the effects of the present invention. Specific examplesof such further optional monomer units include amino acid monomer units,such as glycine monomer unit, (+)-alanine monomer unit, β-alaninemonomer unit, (−)-asparagine monomer unit, (+)-aspartic acid monomerunit, (−)-cysteine monomer unit, (+)-glutamic acid monomer unit,(+)-glutamine monomer unit, (−)-hydroxylysine monomer unit, (−)-leucinemonomer unit, (+)-isoleucine monomer unit, (+)-lysine monomer unit,(−)-methionine monomer unit, (−)-serine monomer unit, (−)-threoninemonomer unit, (+)-valine monomer unit, aminobutyric acid monomer unit,azaserine monomer unit, arginine monomer unit and ethionine monomerunit; polyamine monomer units, such as methylhydrazine monomer unit,monomethylenediamine monomer unit, dimethylenediamine monomer unit,trimethylenediamine monomer unit, tetramethylenediamine monomer unit,pentamethylenediamine monomer unit, hexamethylenediamine monomer unit,heptamethylenediamine monomer unit, oc-tamethylenediamine monomer unit,nonamethylenediamine monomer unit, decamethylenediamine monomer unit,undecamethylenediamine monomer unit and dodecamethylenediamine monomerunit; lactam monomer units, such as β-propiolactam monomer unit,α-pyrrolidone monomer unit, α-piperidone monomer unit, ε-caprolactammonomer unit, α-methyl-caprolactam monomer unit, β-methyl-caprolactammonomer unit, γ-metyl-caprolactam monomer unit, δ-methyl-caprolactammonomer unit, α-methyl-caprolactam monomer unit, N-methyl-caprolactammonomer unit, β,γ-dimethyl-caprolactam monomer unit, γ-ethyl-caprolactammonomer unit, γ-isopropyl-caprolactam monomer unit,ε-isopropyl-caprolactam monomer unit, γ-butyl-caprolactam monomer unit,γ-hexacyclobenzyl-caprolactam monomer unit, ω-enantholactam monomerunit, ω-capryllactam monomer unit, caprylolactam monomer unit andlaurolactam monomer unit. These optional monomer units can be usedindividually or in combination. Among the compounds from which thesemonomer units are derived, when a compound has an asymmetric carbon atomand, hence, exists as optical isomers, any of the isomers may be used.

Further, the glycolic acid copolymer may further comprise a conventionalmonomer unit containing 2 or more of at least one functional groupselected from the group consisting of an isocyanate group and an epoxygroup, as long as the presence of such a monomer unit does not adverselyaffect the effects of the present invention.

It is preferred that the glycolic acid copolymer of the presentinvention has either a configuration (I) comprising glycolic acidmonomer units (a), non-glycolic, hydroxycarboxylic acid monomer units(b) and polyol monomer units (d) or a configuration (II) comprisingglycolic acid monomer units (a), non-glycolic, hydroxycarboxylic acidmonomer units (b), polyol monomer units (d) and polycarboxylic acidmonomer units (e) other than the diglycolic acid monomer units (c). Inany of configuration (I) or (II), it is preferred that the amount ofdiglycolic acid monomer units (c) is zero or a value which is as smallas possible.

When the glycolic acid copolymer of the present invention hasconfiguration (I) or (II) mentioned above, there is an advantage thatthe hydrolysis resistance of the glycolic acid copolymer is improved, orthat flexibility is imparted to a shaped article produced from theglycolic acid copolymer.

When the glycolic acid copolymer of the present invention contains thepolyol monomer unit (d), it is preferred that the amounts of diglycolicacid monomer units (c), polyol monomer units (d) and polycarboxylic acidmonomer units (e) are adjusted so that the difference between the molaramount of hydroxyl groups contained in component (d) and the total molaramount of carboxyl groups contained in components (e) and (c) is 0.10%by mole or less, more advantageously 0.04% by mole or less, based on thetotal molar amount of hydroxyl groups contained in component (d) andcarboxyl groups contained in components (e) and (c). It is especiallypreferred that the molar amount of hydroxyl groups contained incomponent (d) and the total molar amount of carboxyl groups contained incomponents (e) and (c) are substantially the same.

When the glycolic acid copolymer of the present invention hasconfiguration (I) or (II) mentioned above, it is preferred that thetotal amount of the polyol monomer units (d), the polycarboxylic acidmonomer units (e), and the diglycolic acid monomer units (c) is lessthan 2.0% by mole, based on the total molar amount of components (a),(b), (c), (d) and (e). When the total amount of components (d), (e) and(c) is 2.0% by mole or more, a disadvantage is likely to occur in thatthe gas barrier property of the glycolic acid copolymer is lowered. Fromthe viewpoint of improving the hydrolysis resistance of the glycolicacid copolymer of the present invention, it is more preferred that thetotal amount of the polyol monomer units (d), the polycarboxylic acidmonomer units (e), and the diglycolic acid monomer units (c) is frommore than 0.02 to less than 2.0% by mole, based on the total molaramount of components (a), (b), (c), (d) and (e), and the amount of thepolyol monomer units (d) is from 0.02 to less than 2.0% by mole, basedon the total molar amount of components (a), (b), (c), (d) and (e).

When the glycolic acid copolymer of the present invention hasconfiguration (I) or (II) mentioned above, the glycolic acid copolymermay contain a compound unit having, in the unit structure thereof, 3 ormore of at least one member selected from the group consisting of ahydroxyl group and a carboxyl group. Examples of such compound unitsinclude a polyhydroxymonocarboxylic acid monomer unit, amonohydroxypolycarboxylic acid monomer unit, a polyhydroxypolycarboxylicacid monomer unit, polyol monomer unit (d) and polycarboxylic acidmonomer unit (e). From the viewpoint of improving the processability(such as extensibility) of the glycolic acid copolymer, the amount of acompound unit having, in the unit structure thereof, 3 or more of atleast one member selected from the group consisting of a hydroxyl groupand a carboxyl group, is preferably 0.07% by mole or less, morepreferably 0.05% by mole or less, still more preferably 0.03% by mole orless, most preferably 0.02% by mole or less, based on the total molaramount of components of the glycolic acid copolymer.

With respect to the molecular structure of the terminal groups of theglycolic acid copolymer of the present invention, there is no particularlimitation. Examples of terminal groups include a hydroxyl group, acarboxyl group, an acyl group, an alkyl group, an aryl group and analkoxyl group.

Hereinbelow, an explanation is made with respect to an example of themethod for producing the glycolic acid copolymer of the presentinvention; however, the method for producing the glycolic acid copolymerof the present invention is not limited to this example.

That is, in one aspect of the present invention, there is provided amethod for producing a glycolic acid copolymer, which comprises thesteps of:

(A) providing a raw material mixture comprising at least one startingmaterial selected from the group consisting of glycolic acid and aderivative thereof, and a reactant copolymerizable with the at least onestarting material, wherein the reactant comprises at least one memberselected from the group consisting of a non-glycolic, hydroxycarboxylicacid, a derivative thereof and optionally at least one compound selectedfrom the group consisting of a polyol, a polycarboxylic acid and aderivative of the polycarboxylic acid, and subjecting the raw materialmixture to a preliminary polycondensation reaction at a temperature inthe range of from 20 to 160° C., thereby obtaining a reaction mixturecontaining a glycolic acid copolymer prepolymer having a weight averagemolecular weight of from 700 to 5,000,

(B) elevating the temperature of the reaction mixture to 190° C. withina period of 100 minutes as measured from the start of the temperatureelevation in step (B), and

(C) performing a heat treatment of the reaction mixture at a temperaturein the range of from 190 to 300° C. to effect a final polycondensationreaction, wherein the final polycondensation reaction is performed so asto obtain a glycolic acid copolymer having a weight average molecularweight of 10,000 or more, wherein the final polycondensation reaction isperformed under conditions wherein the increasing rate of weight averagemolecular weight of the glycolic acid copolymer being produced ismaintained at 1,000 per hour or more until the weight average molecularweight reaches at least 10,000.

Hereinbelow, explanations are made with respect to the raw materialsused in the method of the present invention for producing a glycolicacid copolymer.

In the present invention, glycolic acid used as a starting material is aglycolic acid monomer or oligomer. With respect to the glycolic acidoligomer, the weight average molecular weight thereof as measured in thesame manner as in the case of the glycolic acid copolymer of the presentinvention is less than 700. Therefore, in the method of the presentinvention, as a starting material, there can be used at least one memberselected from the group consisting of a glycolic acid monomer, aderivative thereof, a glycolic acid oligomer and a derivative thereof.

Specific examples of derivatives of glycolic acid used as a startingmaterial in the method of the present invention include esters derivedfrom glycolic acid and a C₁-C₁₀ alcohol, such as methanol, ethanol,propanol, isopropanol, butanol, pentanol, hexanol, cyclohexanol oroctanol; and glycolide, which is a cyclic dimeric ester of glycolicacid.

As a starting material, glycolic acid and/or a derivative thereof can beused individually or in combination.

In the method of the present invention, the non-glycolic,hydroxycarboxylic acid used as a reactant copolymerizable with thestarting material is a non-glycolic, hydroxycarboxylic acid monomer oroligomer. With respect to the non-glycolic, hydroxycarboxylic acidoligomer, the weight average molecular weight thereof as measured in thesame manner as in the case of the glycolic acid copolymer of the presentinvention is less than 700. Therefore, in the method of the presentinvention, as a reactant copolymerizable with the starting material,there can be used at least one member selected from the group consistingof a non-glycolic, hydroxycarboxylic acid monomer, a derivative thereof,a non-glycolic, hydroxycarboxylic acid oligomer and a derivativethereof.

Examples of non-glycolic, hydroxycarboxylic acids used as a reactantcopolymerizable with glycolic acid and/or a derivative thereof includean aliphatic monohydroxymonocarboxylic acid having 3 or more carbonatoms, an aromatic monohydroxymonocarboxylic acid, an aromaticpolyhydroxymonocarboxylic acid, an aromatic monohydroxypolycarboxylicacid, an aromatic polyhydroxypolycarboxylic acid, an aliphaticpolyhydroxymonocarboxylic acid, an aliphatic monohydroxypolycarboxylicacid, a polyhydroxypolycarboxylic acid, a hydroxycarboxylic acid havinga hetero atom, and lactones. Specific examples of aliphaticmonohydroxymonocarboxylic acids having 3 or more carbon atoms includelactic acid, 2-hydroxybutanoic acid, 2-hydroxypentanoic acid,2-hydroxyhexanoic acid, 2-hydroxyheptanoic acid, 2-hydroxyoctanoic acid,2-hydroxy-2-methylpropanoic acid, 2-hydroxy-2-methylbutanoic acid,2-hydroxy-2-ethylbutanoic acid, 2-hydroxy-2-methylpentanoic acid,2-hydroxy-2-ethylpentanoic acid, 2-hydroxy-2-propylpentanoic acid,2-hydroxy-2-butylpentanoic acid, 2-hydroxy-2-methylhexanoic acid,2-hydroxy-2-ethylhexanoic acid, 2-hydroxy-2-propylhexanoic acid,2-hydroxy-2-butylhexanoic acid, 2-hydroxy-2-pentylhexanoic acid,2-hydroxy-2-methylheptanoic acid, 2-hydroxy-2-ethylheptanoic acid,2-hydroxy-2-propylheptanoic acid, 2-hydroxy-2-butylheptanoic acid,2-hydroxy-2-pentylheptanoic acid, 2-hydroxy-2-hexylheptanoic acid,2-hydroxy-2-methyloctanoic acid, 2-hydroxy-2-ethyloctanoic acid,2-hydroxy-2-propyloctanoic acid, 2-hydroxy-2-butyloctanoic acid,2-hydroxy-2-pentyloctanoic acid, 2-hydroxy-2-hexyloctanoic acid,2-hydroxy-2-heptyloctanoic acid, 3-hydroxypropanoic acid,3-hydroxybutanoic acid, 3-hydroxypentanoic acid, 3-hydroxyhexanoic acid,3-hydroxyheptanoic acid, 3-hydroxyoctanoic acid,3-hydroxy-3-methylbutanoic acid, 3-hydroxy-3-methylpentanoic acid,3-hydroxy-3-ethylpentanoic acid, 3-hydroxy-3-methylhexanoic acid,3-hydroxy-3-ethylhexanoic acid, 3-hydroxy-3-propylhexanoic acid,3-hydroxy-3-methylheptanoic acid, 3-hydroxy-3-ethylheptanoic acid,3-hydroxy-3-propylheptanoic acid, 3-hydroxy-3-butylheptanoic acid,3-hydroxy-3-methyloctanoic acid, 3-hydroxy-3-ethyloctanoic acid,3-hydroxy-3-propyloctanoic acid, 3-hydroxy-3-butyloctanoic acid,3-hydroxy-3-pentyloctanoic acid, 4-hydroxybutanoic acid,4-hydroxypentanoic acid, 4-hydroxyhexanoic acid, 4-hydroxyheptanoicacid, 4-hydroxyoctanoic acid, 4-hydroxy-4-methylpentanoic acid,4-hydroxy-4-methylhexanoic acid, 4-hydroxy-4-ethylhexanoic acid,4-hydroxy-4-methylheptanoic acid, 4-hydroxy-4-ethylheptanoic acid,4-hydroxy-4-propylheptanoic acid, 4-hydroxy-4-methyloctanoic acid,4-hydroxy-4-ethyloctanoic acid, 4-hydroxy-4-propyloctanoic acid,4-hydroxy-4-butyloctanoic acid, 5-hydroxypentanoic acid,5-hydroxyhexanoic acid, 5-hydroxyheptanoic acid, 5-hydroxyoctanoic acid,5-hydroxy-5-methylhexanoic acid, 5-hydroxy-5-methylheptanoic acid,5-hydroxy-5-ethylheptanoic acid, 5-hydroxy-5-methyloctanoic acid,5-hydroxy-5-ethyloctanoic acid, 5-hydroxy-5-propyloctanoic acid,6-hydroxyhexanoic acid, 6-hydroxyheptanoic acid, 6-hydroxyoctanoic acid,6-hydroxy-6-methylheptanoic acid, 6-hydroxy-6-methyloctanoic acid,6-hydroxy-6-ethyloctanoic acid, 7-hydroxyheptanoic acid,7-hydroxyoctanoic acid, 7-hydroxy-7-methyloctanoic acid,8-hydroxyoctanoic acid, 12-hydroxystearic acid and16-hydroxyhexadecanoic acid. A specific example of an aromaticmonohydroxymonocarboxylic acid is hydroxybenzoic acid. Specific examplesof aromatic polyhydroxymonocarboxylic acids include 2,3-dihydroxybenzoicacid, 2,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid,2,6-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid and3,5-dihydroxybenzoic acid. Specific examples of aromaticmonohydroxypolycarboxylic acids include 4-hydroxyisophthalic acid and5-hydroxyisophthalic acid. A specific example of an aromaticpolyhydroxypolycarboxylic acid is 2,5-dihydroxyterephthalic acid.Specific examples of aliphatic polyhydroxymonocarboxylic acids includeglyceric acid, arabinonic acid, mannonic acid and galactonic acid.Specific examples of aliphatic monohydroxypolycarboxylic acids includemalic acid and citric acid. Specific examples ofpolyhydroxypolycarboxylic acids include diglyceric acid andmannosaccharic acid. Specific examples of hydroxycarboxylic acids havinga hetero atom include (2-hydroxyethoxy)acetic acid and(2-hydroxypropoxy)acetic acid. Specific examples of lactones includeβ-propiolactone, γ-butyrolactone, δ-valerolactone and ε-caprolactone.

These non-glycolic, hydroxycarboxylic acids can be used individually orin combination. Further, among the above-mentioned compounds, when acompound has an asymmetric carbon atom and, hence, exists as opticalisomers, any of the isomers may be used.

Examples of derivatives of non-glycolic, hydroxycarboxylic acids includean ester of the above-mentioned hydroxycarboxylic acid with a C₁-C₁₀monofunctional alcohol (e.g., methanol, ethanol, propanol, isopropanol,butanol, pentanol, hexanol or octanol); a cyclic dimeric ester of anon-glycolic, hydroxycarboxylic acid, such as a lactide; and a cyclicdimeric ester of glycolic acid with a non-glycolic, hydroxycarboxylicacid. These compounds may be used individually or in combination.

Among the above-mentioned compounds, from the viewpoint of suppressingthe increase in the water absorbability of the copolymer to therebylower the hydrolysis rate of the copolymer or from the viewpoint ofimproving the processability (such as extensibility) of the copolymerand improving the flexibility of the shaped articles, amonohydroxycarboxylic acid having 3 or more carbon atoms, a derivativeof such a monohydroxycarboxylic acid, or a mixture thereof are preferredin the present invention. It is more preferred that the non-glycolic,hydroxycarboxylic acid is at least one member selected from the groupconsisting of lactic acid, a lactide, a cyclic dimeric ester of glycolicacid with lactic acid, 3-hydroxybutylic acid and/or β-propiolactone,4-hydroxybutylic acid and/or γ-butylolactone, 3-hydroxyvaleric acid,6-hydroxyhexanoic acid and/or ε-caprolactone, 12-hydroxystearic acid,16-hydroxyhexadecanoic acid, derivatives of the above-mentionedaliphatic hydroxycarboxylic acids, and a mixture thereof. From theviewpoint of ease of obtainment, the non-glycolic, hydroxycarboxylicacid is more preferably lactic acid, a lactide, a cyclic dimeric esterof glycolic acid with lactic acid, 6-hydroxyhexanoic acid and/orε-caprolactone, derivatives of the above-mentioned aliphatichydroxycarboxylic acids, or a mixture thereof, most preferably lacticacid, a lactide, a cyclic dimeric ester of glycolic acid with lacticacid, a derivative of lactic acid, or a mixture thereof.

In the present invention, at least one compound selected from the groupconsisting of a polyol, a polycarboxylic acid and a derivative of thepolycarboxylic acid can be used as a raw material which iscopolymerizable with glycolic acid and/or a derivative thereof and anon-glycolic, hydroxycarboxylic acid and/or a derivative thereof. Such apolyol, polycarboxylic acid and a derivative of the polycarboxylic acidare used in amounts within the ranges recited in the present invention.

As a polyol used in the present invention, there can be mentioned acompound having 2 or more hydroxyl groups, and a C₂-C₂₀ polyol ispreferred. Specific examples of polyols include aliphatic diols, such asethylene glycol, 1,3-propanediol, 1,2-propanediol, 1,4-butanediol,2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol,1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-dodecanediol,1,4-cyclohexanediol, 1,2-cyclohexanediol, 1,3-cyclohexanediol andneopentyl glycol; aromatic diols, such as bisphenol A, catechol,resorcinol, 1,2-benzenedimethanol, 1,3-benzenedimethanol and1,4-benzenedimethanol; diols containing a heteroatom, such as diethyleneglycol, triethylene glycol and tetraethylene glycol; aliphatic triols,such as glycerol, 1,2,4-butanetriol, trimethylolethane,trimethylolpropane and butane-1,2,3-triol; aromatic triols, such as1,2,4-benzenetriol and 1,3,5-benzenetriol; and sugars, such as starch,glucose, cellulose, hemicellulose, xylose, arabinose, mannose,galactose, xylitol, arabinitol, mannitol, galactitol, pentaerythritol,chitin, chitosan, dextrin, dextran, carboxymethylcellulose, amylopectinand glycogen.

These polyols can be used individually or in combination. Among theabove-mentioned compounds, when a compound has an asymmetric carbon atomand, hence, exists as optical isomers, any of the isomers may be used.

From the viewpoint of suppressing the occurrence of side reactionsduring the polycondensation reaction or from the viewpoint of improvingthe heat decomposition resistance and heat aging resistance of thecopolymer during melt shaping, it is more preferred that the polyol is adiol having 3 or more carbon atoms. Specific examples of diols having 3or more carbon atoms include aliphatic diols, such as 1,3-propanediol,1,2-propanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol,1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol,1,10-decanediol, 1,12-dodecanediol, 1,4-cyclohexanediol,1,2-cyclohexanediol, 1,3-cyclohexanediol and neopentyl glycol; andaromatic diols, such as bisphenol A, catechol, resorcinol,1,2-benzenedimethanol, 1,3-benzenedimethanol and 1,4-benzenedimethanol.

It is more preferred that the polyol is an aliphatic diol, such as1,3-propanediol, 1,2-propanediol, 1,4-butanediol, 2,3-butanediol,1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol,1,9-nonanediol, 1,10-decanediol, 1,12-dodecanediol, 1,4-cyclohexanediol,1,2-cyclohexanediol, 1,3-cyclohexanediol or neopentyl glycol. The use ofsuch an aliphatic diol is advantageous not only in that an improvementis made in the heat stability and heat aging resistance of the copolymerduring melt shaping, but also in that there is enabled production of ashaped article having excellent flexibility.

A polyol having 3 or more hydroxyl groups in the molecule is used toimprove the melt tension of the copolymer. However, for the copolymer tostably exhibit an improved melt tension, it is more preferred that thepolyol is a compound having 4 or more carbon atoms. Examples of suchcompounds include aliphatic triols, such as 1,2,4-butanetriol,trimethylolethane, trimethylolpropane and butane-1,2,3-triol; aromatictriols, such as 1,2,4-benzenetriol and 1,3,5-benzenetriol; and sugars,such as glucose, xylose, arabinose, mannose, galactose, xylitol,arabinitol, mannitol, galactitol and pentaerythritol.

Among the above-mentioned polyols, more preferred are polyols having 5or more carbon atoms and 3 or less hydroxyl groups in the molecule.Specific examples of such polyols include aliphatic diols, such as1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol,1,9-nonanediol, 1,10-decanediol, 1,12-dodecanediol, 1,4-cyclohexanediol,1,2-cyclohexanediol, 1,3-cyclohexanediol and neopentyl glycol; andaliphatic triols, such as trimethylolethane and trimethylolpropane.

Among these, most preferred is neopentyl glycol.

As a copolymerizable polycarboxylic acid, there can be mentioned acompound having 2 or more carboxyl groups, and a C₂-C₂₀ polycarboxylicacid is preferred. Specific examples of such polycarboxylic acidsinclude aliphatic dicarboxylic acids, such as oxalic acid, malonic acid,gulutaric acid, succinic acid, adipic acid, pimelic acid, suberic acid,azelaic acid, sebacic acid, undecanedicarboxylic acid,dodecanedicarboxylic acid, fumaric acid, maleic acid and1,4-cyclohexanedicarboxylic acid; aromatic dicarboxylic acids, such asphthalic acid, isophthalic acid and terephthalic acid; aliphatictricarboxylic acids, such as propanetricarboxylic acid, trimelliticacid, pyromellitic acid, 1,3,6-hexanetricarboxylic acid; aromatictricarboxylic acids, such as 1,2,3-benzenetricarboxylic acid,1,2,4-benzenetricarboxylic acid and 1,3,5-benzenetricarboxylic acid; andtetracarboxylic acids, such as ethylenediaminetetraacetic acid. Thesecompounds can be used individually or in combination.

Examples of derivatives of the polycarboxylic acids include an ester ofthe polycarboxylic acid with a C₁-C₁₀ monofunctional alcohol (e.g.,methanol, ethanol, propanol, isopropanol, butanol, pentanol, hexanol oroctanol); an ester of the polycarboxylic acid with glycolic acid; and ananhydride of the polycarboxylic acid.

Among the above-mentioned polycarboxylic acids, more preferred arealiphatic dicarboxylic acids, such as oxalic acid, malonic acid,gulutaric acid, succinic acid, adipic acid, pimelic acid, suberic acid,azelaic acid, sebacic acid, undecanedicarboxylic acid,dodecanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid; aromaticdicarboxylic acids, such as phthalic acid, isophthalic acid andterephthalic acid; aliphatic tricarboxylic acids, such aspropanetricarboxylic acid, trimellitic acid, pyromellitic acid and1,3,6-hexanetricarboxylic acid; aromatic tricarboxylic acids, such as1,2,3-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic acid and1,3,5-benzenetricarboxylic acid. Derivatives of these polycarboxylicacids are also more preferred.

From the viewpoint of obtaining a shaped article having excellentflexibility, it is most preferred that a polycarboxylic acid or aderivative thereof is selected from the group consisting of aliphaticdicarboxylic acids, such as oxalic acid, malonic acid, gulutaric acid,succinic acid, adipic acid, pimelic acid, suberic acid, azelaic acid,sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid and1,4-cyclohexanedicarboxylic acid, and a derivative thereof; andaliphatic tricarboxylic acids, such as propanetricarboxylic acid,trimellitic acid, pyromellitic acid and 1,3,6-hexanetricarboxylic acid,and a derivative thereof.

In addition, other compounds, such an amino acid, a polyamine and alactam, may be used as a comonomer in an amount which does not adverselyaffect the properties of the present invention.

As an amino acid used in the present invention, a C₂-C₂₀ amino acid ispreferred. Specific examples of such amino acids include glycine,(+)-alanine, β-alanine, (−)-asparagine, (+)-aspartic acid, (−)-cysteine,(+)-glutamic acid, (+)-glutamine, (−)-hydroxylysine, (−)-leucine,(+)-isoleucine, (+)-lysine, (−)-methionine, (−)-serine, (−)-threonine,(+)-valine, aminolactic acid, azaserine, alginine and ethionine.

As a polyamine used in the present invention, a C₁-C₂₀ polyamine ispreferred. Specific examples of such polyamines include methylhydrazine,monomethylenediamine, dimethylenediamine, trimethylenediamine,tetramethylenediamine, pentamethylenediamine, hexamethylenediamine,heptamethylenediamine, octamethylenediamine, nonanemethylenediamine,decamethylenediamine, undecamethylenediamine and dodecamethylenediamine.

As a lactam used in the present invention, a C₂-C₂₀ lactam is preferred.Specific examples of such lactams include glycine anhydride,β-propiolactam, α-pyrrolidone, α-piperidone, ε-caprolactam,α-methyl-caprolactam, α-methyl-caprolactam, γ-methyl-caprolactam,α-methyl-caprolactam, ε-methyl-caprolactam, N-methyl-caprolactam,β,γ-dimethyl-caprolactam, γ-ethyl-caprolactam, γ-isopropyl-caprolactam,ε-isopropyl-caprolactam, γ-butylcaprolactam,γ-hexacyclobenzyl-caprolactam, ω-enantholactam, ω-capryllactam,caprylolactam, laurolactam and a dimer of caprolactone.

Among the above-mentioned compounds, when a compound has an asymmetriccarbon atom and the compound exists in a D-form, an L-form or a mixtureof D- and L-forms, any one of these forms may be used.

With respect to the forms of the raw materials used (i.e., glycolicacid, a derivative of glycolic acid, and a compound copolymerizable withglycolic acid and/or derivative of glycolic acid), there is noparticular limitation. The raw materials may be in the form of asolution (such as an aqueous solution), crystals or a liquid. When theraw material is used in the form of a solution, there is no particularlimitation with respect to the concentration thereof in the solution,but it is preferred that the raw material concentration of the solutionis at least 40% by weight, more advantageously at least 50% by weight,most advantageously at least 60% by weight.

In the method of present invention, the formulation of the raw materialmixture is appropriately selected so as to obtain the glycolic acidcopolymer of the present invention after the polycondensation reaction.However, it is preferred that the raw material mixture satisfies thefollowing formulae (1) to (3):0.8≦X¹≦0.95  (1),0.05≦X²  (2), andX¹ +X ² +X ₃ +X ⁴=1  (3)wherein:

-   -   X¹ represents the calculated molar ratio of the at least one        starting material selected from the group consisting of glycolic        acid and a derivative thereof,    -   X² represents the calculated molar ratio of the at least one        member selected from the group consisting of a non-glycolic,        hydroxycarboxylic acid and a derivative thereof,    -   X³ represents the calculated molar ratio of an optional polyol,    -   X⁴ represents the calculated molar ratio of at least one        optional raw material selected from the group consisting of a        polycarboxylic acid and a derivative thereof,        -   the calculated molar ratio of each raw material being            defined as the ratio of the molar amount of the unit            structure obtained by hydrolysis of each raw material to the            total molar amount of the unit structures of all raw            materials, and        -   each of X³ and X⁴ is independently 0 or more.

Hereinbelow, explanations are given with respect to “monomer units” usedin the present invention and “calculated molar ratio” of each rawmaterial used in step (A) of the method of the present invention.

In the present invention, the term “monomer unit” (of a compound) isused to indicate a minimum unit structure which is obtained byhydrolysis of a copolymer or a compound used as a raw material for thecopolymer. More specifically, for example, with respect to glycolic acidand a derivative thereof, the term “glycolic acid monomer unit”(contained in the copolymer of the present invention and in glycolicacid and a derivative thereof) means a unit structure represented by thefollowing formula (I):

On the other hand, with respect to a non-glycolic, hydroxycarboxylicacid and a derivative thereof, for example lactic acid and a derivativethereof, the term “lactic acid monomer unit” means a unit structurerepresented by the following formula (II):

Further, with respect to a polycarboxylic acid and a derivative thereof,for example adipic acid and a derivative thereof, the term “adipic acidmonomer unit” means a unit structure represented by the followingformula (III):

In the present invention, the term “calculated molar ratio” is used tomean the ratio of the molar amount of the unit structure (e.g., a unitstructure represented by the formula (I), (II) or (III) above) of eachraw material compound (i.e., the starting material or reactant mentionedabove) to the total molar amount of the unit structures of all rawmaterial compounds. In the determination of the calculated molar ratio,with respect to a raw material compound used in an amount such that themolar ratio of the unit structure thereof to the total of the unitstructures of all raw material compounds is less than 0.00005, the molarratio of the unit structure of the raw material compound is consideredto be 0.

Further, in the determination of the calculated molar ratio, the molaramounts of monofunctional compounds (e.g., monofunctional alcohols andmonofunctional carboxylic acids) derived from raw material compoundsused are not taken into consideration in the calculation of the totalmolar amount of the unit structures of all raw material compounds. Thereason is as follows. For example, when an ester of a monofunctionalC₁-C₁₀ alcohol with a monofunctional carboxylic acid is used as a rawmaterial compound, some monofunctional alcohols or monofunctionalcarboxylic acids may be liberated by hydrolysis or the like. As aresult, the liberated monofunctional alcohols or monofunctionalcarboxylic acids may be present in the raw material mixture. Therefore,such monofunctional alcohols and monofunctional carboxylic acids are nottaken into consideration in the determination of the calculated molarratio.

In the present invention, with respect to diglycolic acid and/ordiglycolic acid monomer units (i.e., diglycolic acid monomer unitspresent in the ester formed by the condensation of diglycolic acid andglycolic acid) contained in a raw material mixture comprising at leastone starting material selected from the group consisting of glycolicacid and a derivative thereof, and a reactant copolymerizable with theat least one starting material, wherein the reactant comprises at leastone member selected from the group consisting of a non-glycolic,hydroxycarboxylic acid, a derivative thereof and optionally at least onecompound selected from the group consisting of a polyol, apolycarboxylic acid and a derivative of the polycarboxylic acid, it isimportant that the calculated molar ratio of diglycolic acid and/ordiglycolic acid monomer units is less than 0.001, preferably less than0.0005, more preferably less than 0.0003. When the calculated molarratio of diglycolic acid and/or diglycolic acid monomer units is 0.001or more, it is difficult to obtain the glycolic acid copolymer of thepresent invention.

Further, when the calculated molar ratio of glycolic acid and/or aderivative thereof and the calculated molar ratio of a non-glycolic,hydroxycarboxylic acid and/or a derivative thereof satisfy the formulae(1) and (2) above, respectively, and also the calculated molar ratio ofa polycarboxylic acid and/or a derivative thereof satisfies thebelow-mentioned formula (4), for obtaining an advantage in that acopolymer having high molecular weight and high hydrolysis resistance ora copolymer having high flexibility can be produced at a highpolymerization rate, it is preferred that the calculated molar ratio ofa polyol is in a range such that the below-mentioned formula (5) issatisfied, more advantageously in a range such that the below-mentionedformula (11) is satisfied, still more advantageously in a range suchthat the below-mentioned formula (12) is satisfied: $\begin{matrix}{{\frac{X^{4}}{X^{1} + X^{2}} \leq 0.001},} & (4) \\{{0 < \frac{X^{3}}{X^{1} + X^{2}} \leq 0.01},} & (5) \\{{0.0002 \leq \frac{X^{3}}{X^{1} + X^{2}} \leq 0.005},\quad{and}} & (11) \\{{0.0002 \leq \frac{X^{3}}{X^{1} + X^{2}} \leq 0.003},} & (12)\end{matrix}$

-   -   wherein X¹ to X⁴ are as defined for formulae (1) to (3) above,        provided that X³ is more than 0, and X⁴ is 0 or more.

On the other hand, when the calculated molar ratio of glycolic acidand/or a derivative thereof and the calculated molar ratio of anon-glycolic, hydroxycarboxylic acid and/or a derivative thereof satisfythe formulae (1) and (2) above, respectively, and also the calculatedmolar ratio of a polycarboxylic acid and/or a derivative thereofsatisfies the below-mentioned formula (6), it is preferred that thecalculated molar ratio of a polyol is in a range such that thebelow-mentioned formula (7) is satisfied, more advantageously in a rangesuch that the below-mentioned formula (13) is satisfied, still moreadvantageously in a range such that the below-mentioned formula (14) issatisfied: $\begin{matrix}{{0.001 < \frac{X^{4}}{X^{1} + X^{2}} \leq 0.088},} & (6) \\{{1 \leq \frac{X^{3}}{X^{4}} \leq 2},} & (7) \\{{1 \leq \frac{X^{3}}{X^{4}} \leq 1.7},{and}} & (13) \\{{1 \leq \frac{X^{3}}{X^{4}} \leq 1.5},} & (14)\end{matrix}$

-   -   wherein X¹ to X⁴ are as defined for formulae (1) to (3) above,        provided that each of X³ and X⁴ is more than 0.

Further, for producing a glycolic acid copolymer having excellent gasbarrier property, it is especially preferred that the calculated molarratios of glycolic acid and/or a derivative thereof, a non-glycolic,hydroxycarboxylic acid and/or a derivative thereof, a polycarboxylicacid and a polyol are within ranges such that the following formula (8)is satisfied: $\begin{matrix}{{0.0002 \leq \frac{X^{3} + X^{4}}{X^{1} + X^{2} + X^{3} + X^{4}} < 0.02},} & (8)\end{matrix}$

-   -   wherein X¹ to X⁴ are as defined for formulae (1) to (3) above,        provided that X³ is more than 0, and X⁴ is 0 or more.

In the present invention, when the reactant comprises a compound unithaving, in the unit structure thereof, 3 or more of at least one memberselected from the group consisting of a hydroxyl group and a carboxylgroup, such as a polyhydroxymonocarboxylic acid, amonohydroxypolycarboxylic acid, a polyhydroxypolycarboxylic acid, apolyol or a polycarboxylic acid, it is preferred that the calculatedmolar ratio of the reactant is 0.0007 or less, more advantageously0.0005 or less, still more advantageously 0.0003 or less. When thecalculated molar ratio of the reactant exceeds the above-mentionedrange, it is possible that the processability (such as extensibility) ofthe obtained copolymer is lowered.

Polycondensation reaction can be performed without using a catalyst;however, a catalyst may be optionally used for increasing the reactionrate.

As examples of catalysts, there can be mentioned metals belonging toGroups 1 to 5, 8 to 10, 14 and 15 of the Periodic Table, and compoundscontaining these metals, such as metal salts, metal oxides, metalhydroxides, metal alkoxides and metal sulfonates. (The “Periodic Table”mentioned herein is that prescribed in the IUPAC (International Union ofPure and Applied Chemistry) nomenclature system (1989).) Specificexamples of catalysts include metals, such as titanium, zirconium,niobium, tungsten, zinc, germanium, tin and antimony; metal oxides, suchas magnesium oxide, titanium oxide, zinc oxide, germanium oxide, silica,alumina, tin oxide and antimony oxide; metal salts, such as tinfluoride, antimony fluoride, magnesium chloride, aluminum chloride, zincchloride, stannous chloride, stannic chloride, stannous bromide, stannicbromide, aluminum sulfate, zinc sulfate, tin sulfate, magnesiumcarbonate, calcium carbonate and zinc carbonate; metal hydroxides, suchas lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesiumhydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide,aluminum hydroxide, zirconium hydroxide, iron hydroxide, cobalthydroxide, nickel hydroxide, copper hydroxide and zinc hydroxide; metalcarboxylates, such as magnesium acetate, aluminum acetate, zinc acetate,tin acetate, tin octanoate, tin stearate, iron lactate and tin lactate;alkoxides of metals, such as magnesium, lanthanoid, titanium, hafnium,iron, germanium, tin and antimony; organometallic compounds, such asdibutyltin oxide; organosulfonates, such as tin methanesulfonate, tintrifluoromethanesulfonate and tin p-toluenesulfonate; and ion exchangeresins, such as Amberlite and Dowex.

Further examples of catalysts include inorganic acids, such ashydrochloric acid, perchloric acid, nitric acid, nitrous acid, sulfuricacid, sulfurous acid, phosphoric acid, phosphorous acid andpolyphosphoric acid; and organic acids, such as p-toluenesulfonic acid,naphthalenesulfonic acid and methanesulfonic acid.

The catalyst usable in the present invention is not limited to thosementioned above. The above-mentioned catalysts can be used individuallyor in combination.

In the present invention, a catalyst can be used, for example, bydirectly adding the catalyst to the raw material monomers or to themonomer solutions including aqueous monomer solutions, or by adding thecatalyst to a polycondensation product just after the productionthereof. Further, if desired, a catalyst can be used by a method inwhich the catalyst is subjected to hydrolysis in the presence of waterand/or a hydroxycarboxylic acid, and the resultant hydrolysis product isadded to the raw material monomers or a polycondensation product. Withrespect to the molecular weight and the like of the above-mentionedpolycondensation product, there is no particular limitation, so long asthe polycondensation product can be subjected to further meltpolycondensation.

With respect to the amount of catalyst to be used, it is preferred thatthe catalyst is used in an amount within the range of from 1×10⁻¹⁰ moleto 1×10⁻² mole per g of the monomers used as raw materials, in terms ofthe metal atoms contained in the catalyst. When the amount of thecatalyst used is less than 1×10⁻² mole per g of the monomers used as rawmaterials, in terms of the metal atoms contained in the catalyst, theeffect of increasing the polycondensation reaction rate cannot be fullyexhibited. On the other hand, when the amount of the catalyst used ismore than 1×10⁻² mole per g of the monomers used as raw materials, interms of the metal atoms contained in the catalyst, marked occurrence ofside reactions, such as discoloration, is likely to be caused.

For suppressing the occurrence of discoloration caused by the heatdeterioration during a polycondensation reaction, the reaction can beperformed using a discoloration inhibitor. A discoloration inhibitor maybe used as such, or by dissolving or dispersing it in an appropriateliquid prior to use. With respect to the timing of introducing adiscoloration inhibitor to the reaction system, there is no particularlimitation, and a discoloration inhibitor can be introduced to thereaction system at any time between the time of concentration of monomersolutions or condensation of raw material monomers and the time ofsubstantial completion of the polycondensation reaction. Theintroduction of a discoloration inhibitor may be performed at a time orportionwise.

Preferred examples of discoloration inhibitors used in thepolycondensation reaction include phosphoric acid compounds, such asphosphoric acid, trimethyl phosphate, triethyl phosphate, triphenylphosphate, polyphosphoric acid monoethyl ester, polyphosphoric aciddiethyl ester, pyrophosphoric acid, triethyl pyrophosphate,hexamethylpyrophosphoric amide, phosphorous acid, triethyl phosphite,triphenyl phosphite, tris(2-tert-butylphenyl)phosphite,tris(2,4-di-tert-butylphenyl)phosphite,tris(2,5-di-tert-butylphenyl)phosphite,tris(2-tert-butyl-4-methylphenyl)phosphite,tris(2-tert-butyl-5-methylphenyl)phosphite,tris(2-tert-butyl-4,6-dimethylphenyl)phosphite, trisnonylphenylphosphite, tris(monononylphenyl)phosphite andtris(dinonylphenyl)phosphite.

These discoloration inhibitors can be used individually or incombination. The amount of discoloration inhibitor to be used ispreferably from 0.0005 to 10% by weight, more preferably from 0.005 to6% by weight, based on the total weight of the raw material monomers.Even when a discoloration inhibitor is used in an amount of more than10% by weight, based on the total weight of the raw material monomers,the effect of suppressing the occurrence of discoloration cannot beincreased. On the other hand, when a discoloration inhibitor is used inan amount of less than 0.0005% by weight, based on the total weight ofthe raw material monomers, the effect of suppressing the occurrence ofdiscoloration is not satisfactory. With respect to the timing ofintroducing these discoloration inhibitors, there is no particularlimitation. Discoloration inhibitors may be added directly to the rawmaterial mixture or may be introduced into the polycondensation reactionsystem during the polycondensation reaction or after completion of thepolycondensation reaction.

Next, explanations are made with respect to steps (A), (B) and (C) ofthe method for producing the glycolic acid copolymer of the presentinvention.

<Step (A)>

In step (A), a raw material mixture comprising at least one startingmaterial selected from the group consisting of glycolic acid and aderivative thereof, and a reactant copolymerizable with the at least onestarting material is provided, wherein the reactant comprises at leastone member selected from the group consisting of a non-glycolic,hydroxycarboxylic acid, a derivative thereof and optionally at least onecompound selected from the group consisting of a polyol, apolycarboxylic acid and a derivative of the polycarboxylic acid, and theraw material mixture is subjected to a preliminary polycondensationreaction at a temperature in the range of from 20 to 160° C., preferablyfrom 50 to 160° C., more preferably from 80 to 160° C., therebyobtaining a reaction mixture containing a glycolic acid copolymerprepolymer having a weight average molecular weight of from 700 to5,000, preferably from 1,000 to 4,000, more preferably from 1,200 to3,000.

When the polycondensation reaction temperature is less than 20° C., thereaction rate becomes extremely low. On the other hand, when thepolycondensation reaction temperature is more than 160° C., thepolycondensation reaction rate becomes high; however, the formation ofdiglycolic acid monomer units in the glycolic acid copolymer prepolymerby the occurrence of a side reaction is promoted, thus causing problemsnot only in that the polymerization of the glycolic acid copolymerprepolymer in the subsequent polycondensation step is rendereddifficult, but also in that the heat stability of the obtained glycolicacid copolymer is lowered.

When the weight average molecular weight of the glycolic acid copolymerprepolymer obtained in step (A) is less than 700, such a low weightaverage molecular weight is insufficient for suppressing the formationof diglycolic acid monomer units in the glycolic acid copolymer duringthe subsequent polycondensation reaction performed at high temperatures.When the weight average molecular weight of the glycolic acid copolymerprepolymer obtained in step (A) is more than 5,000, depending on thecomposition of the glycolic acid copolymer prepolymer and the types andmolecular weights of the comonomers, the glycolic acid copolymerprepolymer is likely to deposit, rendering difficult the continuation ofthe polycondensation reaction in a molten state.

In step (A), it is not necessary that the reaction be performed at aconstant temperature, as long as the reaction temperature is maintainedin the range of from 20 to 160° C. That is, the reaction may beperformed while gradually elevating or lowering the reactiontemperature, or while performing such temperature manipulations incombination. In the subsequent step (B), the temperature of the reactionmixture is elevated to 190° C. within a period of 100 minutes asmeasured from the start of the temperature elevation in step (B). Thestarting point of the temperature elevation in step (B) (i.e., the endpoint of step (A)) is defined as the point in time at which thetemperature elevation is started while the weight average molecularweight of the glycolic acid copolymer prepolymer is still in the rangeof from 700 to 5,000. However, in the case where the temperatureelevation is repeated several times or an operation comprising elevationand lowering of the temperature is performed at least one time after theweight average molecular weight of the glycolic acid copolymerprepolymer reached 700, the starting point of the temperature elevationin step (B) (i.e., the end point of step (A)) is defined as the startingpoint of the last temperature elevation.

The reaction in step (A) is preferably performed in an atmosphere of atleast one inert gas selected from the group consisting of nitrogen gas,helium gas, neon gas, argon gas, krypton gas, xenon gas, carbon dioxidegas and a gaseous saturated C₁-C₄ lower hydrocarbon, and/or underreduced pressure. When the reaction in step (A) is performed underreduced pressure, the pressure is generally in the range of from 1.3 Pato 1.014×10⁵ Pa, depending on the composition of the glycolic acidcopolymer prepolymer, the types of comonomers and the reactiontemperature. When performing the reaction in step (A), it is preferredto employ a method in which the reaction is performed under atmosphericpressure and optionally under a stream of an inert gas, or a method inwhich the reaction is performed under reduced pressure and optionallyunder a stream of an inert gas, or a combination of these methods. It isalso preferred to employ a method in which the polycondensation reactionis performed while changing stepwise the reaction temperature and/or thepressure. The reaction can be performed using a single reactor or acombination of a plurality of reactors.

<Step (B)>

In step (B), the temperature of the reaction mixture obtained in step(A) containing a glycolic acid copolymer prepolymer having a weightaverage molecular weight of 700 to 5,000 is elevated from the reactiontemperature employed in step (A) to 190° C. within a period of 100minutes, preferably within a period of 80 minutes, more preferablywithin a period of 60 minutes, as measured from the start of thetemperature elevation in step (B). There is no particular limitationwith respect to the lower limit of the time for the temperatureelevation. However, the lower limit of the time for the temperatureelevation is preferably 0.1 second, more preferably 1 minute.

When the reaction temperature after performing the temperature elevationis less than 190° C., or when the temperature elevation time to reach190° C. is more than 100 minutes, the reaction rate of the formation ofdiglycolic acid monomer units is not satisfactorily low, as compared tothe polycondensation reaction rate and, hence, a problem arises in thata high molecular weight glycolic acid copolymer exhibiting excellentmelt heat stability cannot be obtained by the polycondensation reactionin the subsequent step (C).

In step (B), the reaction temperature is elevated from that employed instep (A) to 190° C. within a period of 100 minutes. It is not necessarythat the temperature elevation rate be constant. That is, the reactiontemperature may be elevated gradually or, alternatively, there may beemployed temperature elevation conditions wherein the temperatureelevation is temporarily stopped to temporarily maintain a constanttemperature, followed by resuming the temperature elevation, to therebyelevate the temperature to 190° C.

Further, in step (B), it is preferred that the temperature elevation isperformed under conditions wherein the average increasing rate of weightaverage molecular weight of the glycolic acid copolymer prepolymer is300 per hour or more as measured from the end point of step (A) (i.e.,the starting point of step (B)) to the point in time at which thereaction temperature reaches 190° C. It is preferred that the increasingrate of weight average molecular weight is as high as possible, from theviewpoint of suppressing the formation of diglycolic acid monomer unitsin the glycolic acid copolymer being produced.

There is no particular limitation with respect to the method of thetemperature elevation in step (B). For example, when at least a portionof the reaction in step (A) and the reaction in step (C) subsequent tostep (B) are performed using the same reactor, the temperature elevationin step (B) can be conducted in the reactor while continuing thepolycondensation reaction under reduced pressure using the reactor or,alternatively, the temperature elevation in step (B) can be conducted bya method in which a reactor having a heat exchanger connected thereto isused, and the reaction mixture is withdrawn from the reactor andcirculated through the heat exchanger to elevate the temperature of thereaction mixture, whereupon the temperature-elevated reaction mixture isrecycled to the reactor, optionally followed by further temperatureelevation in the reactor (that is, the temperature of the reactionmixture is elevated by the reactor and/or the heat exchanger). When thereaction in step (A) and the reaction in step (C) are performed usingdifferent reactors, the temperature elevation of step (B) can beperformed while transferring the reaction mixture from the reactor usedin step (A) to the reactor used in step (C) through a pipeline. Thesemethods may be used in combination.

<Step (C)>

In step (C), a heat treatment of the reaction mixture is performed at atemperature in the range of from 190 to 300° C. to effect a finalpolycondensation reaction, wherein the final polycondensation reactionis performed so as to obtain a glycolic acid copolymer having a weightaverage molecular weight of 10,000 or more, wherein the finalpolycondensation reaction is performed under conditions wherein theincreasing rate of weight average molecular weight of the glycolic acidcopolymer being produced is maintained at 1,000 per hour or more,preferably 2,000 per hour or more, more preferably 3,000 per hour ormore, until the weight average molecular weight reaches at least 10,000.

The reaction temperature is preferably in the range of from 190 to 250°C., more preferably from 190 to 230° C.

The increasing rate (hereinafter, frequently abbreviated as “M”) ofweight average molecular weight per hour in step (C) which is performedafter the reaction temperature reaches 190° C. until the weight averagemolecular weight of the glycolic acid copolymer being produced reachesat least 10,000, means a value represented by the following formula:M=(10,000−Mw1)/T1

-   -   wherein:    -   Mw1 represents the weight average molecular weight at the point        in time at which the reaction temperature reaches 190° C., and        T1 represents the time (hour) which is taken by the weight        average molecular weight to reach 10,000 after the reaction        temperature reaches 190° C.

When the reaction temperature for producing the glycolic acid copolymerhaving a weight average molecular weight of 10,000 or more is less than190° C., or when the increasing rate of weight average molecular weightis maintained at less than 1,000 per hour until the weight averagemolecular weight reaches at least 10,000 after the reaction temperaturereaches 190° C. or more, the reaction rate of the formation ofdiglycolic acid monomer units is not satisfactorily low, as compared tothe polycondensation reaction rate and, hence, a problem arises in thata high molecular weight glycolic acid copolymer exhibiting excellentmelt heat stability can not be obtained. On the other hand, when thepolycondensation reaction is performed at a temperature of more than300° C., the occurrence of discoloration of the glycolic acid copolymer,due to the heat decomposition, becomes marked.

In step (C), the increasing rate of weight average molecular weight ismaintained at 1,000 per hour or more until the weight average molecularweight reaches at least 10,000. It is not necessary that the reactiontemperature be constant in the range of from 190 to 300° C. That is, thereaction temperature may be gradually elevated or lowered, or suchtemperature manipulations may be performed in combination.

There is no particular limitation with respect to the method foradjusting the polycondensation reaction rate to fall within the rangerequired in the method of the present invention. For example, thepolycondensation reaction rate required in the method of the presentinvention can be attained by controlling the reaction conditions, suchas the reaction temperature, the reaction pressure, the interfacial areabetween the glycolic acid copolymer in a molten state and the gaseousphase during the reaction (i.e., molten polymer/gaseous phaseinterfacial area), and the degree of agitation of the glycolic acidcopolymer in a molten state during the reaction.

The reaction can be performed under a stream of at least one inert gasselected from the group consisting of nitrogen gas, helium gas, neongas, argon gas, krypton gas, xenon gas, carbon dioxide gas and a gaseoussaturated C₁-C₄ lower hydrocarbon, and/or under reduced pressure. Forincreasing the polycondensation reaction rate, the reaction ispreferably performed under reduced pressure. When the reaction isperformed under reduced pressure, the pressure is varied depending onthe composition of the glycolic acid copolymer, the types of comonomers,the reaction temperature and the type and amount of a catalyst; however,the pressure is generally in the range of from 1.3 Pa to 1.3×10³ Pa,preferably from 1.3×10 Pa to 9.3×10² Pa, more preferably from 6.5×10² Pato 6.7×10² Pa. When the pressure is within the above-mentioned pressurerange, the reaction may be performed under a stream of an inert gas.Further, the operating conditions in this step, such as the reactiontemperature and reaction pressure, may be varied within appropriateranges as long as the requirements (concerning the temperature and theincreasing rate of weight average molecular weight) in the method of thepresent invention are satisfied.

With respect to the interfacial area between the glycolic acid copolymerin a molten state and the gaseous phase during the reaction (i.e.,molten polymer/gaseous phase interfacial area), there is no particularlimitation. The larger this interfacial area, the easier thedistillation off of condensation water from the reaction system, thusfacilitating the polycondensation reaction. Therefore, it is preferredthat the interfacial area between the glycolic acid copolymer in amolten state and the gaseous phase during the reaction, is as large aspossible.

On the other hand, with respect to the degree of agitation of theglycolic acid copolymer in a molten state during the reaction, thehigher the degree of agitation, the easier the distillation off ofcondensation water from the reaction system, thus facilitating thepolycondensation reaction. Therefore, it is preferred that the degree ofagitation of the glycolic acid copolymer in a molten state during thereaction is as high as possible.

In step (C), with respect to the time for the polycondensation reaction,there is no particular limitation, as long as a glycolic acid copolymerhaving a weight average molecular weight of 10,000 or more can beproduced under conditions wherein the increasing rate of weight averagemolecular weight of the glycolic acid copolymer is maintained at 1,000per hour or more until the weight average molecular weight of theglycolic acid copolymer reaches at least 10,000. For example, thereaction time is preferably in the range of from 10 minutes to 9 hours,more preferably from 30 minutes to 4.5 hours, still more preferably from45 minutes to 3.5 hours.

In step (C), the glycolic acid copolymer of the present invention havinga weight average molecular weight of 50,000 or more can be obtained byappropriately selecting the reaction temperature, the reaction time, thereaction apparatus and the like. Alternatively, the glycolic acidcopolymer of the present invention having a weight average molecularweight of 50,000 or more can be obtained by a method in which, afterobtaining a glycolic acid copolymer having a weight average molecularweight of less than 50,000 in step (C), the polycondensation reaction iscontinued under conditions which do not satisfy the requirements of step(C), for example, at a temperature lower than the temperature rangerequired in step (C). Needless to say, the glycolic acid copolymer ofthe present invention having a weight average molecular weight of 50,000or more can also be obtained by a method in which, after obtaining aglycolic acid copolymer having a weight average molecular weight of50,000 or more in step (C), the polycondensation reaction is continuedunder conditions which do not satisfy the requirements of step (C), forexample, at a temperature lower than the temperature range required instep (C), thereby further increasing the weight average molecular weightof the glycolic acid copolymer being produced.

Hereinbelow, an explanation is made with respect to an additionalpolycondensation reaction performed after step (C).

After completion of step (C), with respect to the glycolic acidcopolymer obtained in step (C), the polycondensation reaction may becontinued at a temperature in the range of from 190 to 300° C.

When the polycondensation reaction is continued, the reaction time canbe arbitrarily chosen, depending on the composition of the desiredglycolic acid copolymer, the types of comonomers, the molecular weightof the desired glycolic acid copolymer, the type of the polycondensationreactor used and the reaction conditions. The reaction time ispreferably in the range of from 1 minute to 200 hours, more preferablyfrom 10 minutes to 150 hours, still more preferably from 1 to 120 hours,most preferably from 1.5 to 100 hours.

In the additional polycondensation reaction performed after step (C), ahigh molecular weight glycolic acid copolymer having a weight averagemolecular weight of from more than 10,000 to 1,000,000 can be obtainedby appropriately selecting the type and amount of a catalyst, thereactor and the reaction conditions.

Further, in the present invention, after completion of step (C), aconventional bi or more-functional compound having at least one memberselected from the group consisting of an isocyanate group and an epoxygroup may be added to the glycolic acid copolymer in a molten state,wherein the amount of the compound is chosen so as not to adverselyaffect the effects of the present invention. The amount of the compoundis in the range of from 0.05 to 5 parts by weight, relative to 100 partsby weight of the glycolic acid copolymer.

The reactions in steps (A), (B) and (C), and the additionalpolycondensation reaction performed after step (C) may be performedusing the same reactor or different reactors. Further, each of thesereactions can be performed in batch-wise manner or in continuous manner.

With respect to any of the polycondensation reaction performed in themethod of the present invention and the additional polycondensationreaction performed after step (C) of the method of the presentinvention, the reactor used is not particularly limited. For example,the following reactors can be used: an agitation type reactor vesseloptionally provided with a baffle plate; a surface-renewal agitationtype reactor vessel; a wiped film type reactor; a centrifugal wiped filmevaporation type reactor; a surface-renewal type twin-screw kneadingreactor; a wall-wetting fall rector; a free-fall polymerizer having aperforated plate; a guide-wetting fall polymerizer having a perforatedplate and at least one guide (e.g., a wire) provided in association withthe perforated plate (e.g., a wire-wetting fall reactor having aperforated plate) These reactors can be used individually or incombination. Further, these reactors can be used in combination with aconventional heat exchanger as a means for achieving the temperatureelevation rate required in the method of the present invention.

When an agitation type reactor vessel is used as a reactor, if desired,the agitation type reactor vessel may be provided with a baffle plateand a conventional impeller.

There is no particular limitation with respect to the shape andinstallation method of a baffle plate. For reference information ofexamples of the shapes and installation methods of baffle plates,reference can be made, for example, to “Kagaku Sochi (ChemicalEquipment)”, September edition, p. 13 (published by Kogyo ChosakaiPublishing Inc., Japan, 1981).

Specific examples of impellers include a propeller, an angled bladepaddle, a plane blade paddle, a pitched blade paddle, a disc turbineblade paddle, a curved blade paddle, a Pfaudler type impeller, aBulmarzin type impeller, a max blend impeller, a helical screw impeller,a helical ribbon impeller, an anchor impeller, a screw anchor impeller,a paddle impeller, a helical impeller and the like described in “KagakuKougaku Benran (Chemical Engineering Handbook)” 5th edition, 5th print,p. 887-919 (published by MARUZEN CO., LTD., Japan, 1995); a doubleribbon impeller described in “Kagaku Sochi (Chemical Equipment)”September edition, p. 11-17 (published by Kogyo Chosakai PublishingInc., 1981) and “LOGBORN” (tradename) manufactured and sold by ShinkoPantec Co., Ltd., Japan.

Specific examples of surface-renewal agitation type reactor vesselsinclude “Advance Ribbon Reactor” (AR) (tradename) and “Vertical ConeReactor” (VCR) (tradename), both manufactured and sold by MitsubishiHeavy Industries, Ltd., Japan; “LOGBORN” (tradename) manufactured andsold by Shinko Pantec Co., Ltd., Japan; “Lattice-Type Twisting BladePolymerizer” (tradename) manufactured and sold by Hitachi, Ltd., Japan;“Super Blend” (tradename) (a concentric biaxial mixing vessel)manufactured and sold by Sumitomo Heavy Industries, Ltd., Japan; and“Vistar” (tradename) (an agitator for high-viscosity liquids)manufactured and sold by Nissen Co., Ltd., Japan.

Specific examples of surface-renewal type twin-screw kneading reactorsinclude “Horizontal Biaxial Reactor for High-Viscosity Liquids” (HVR)(tradename), “Self-Cleaning Type Reactor” (SCR) (tradename) and “NewSelf-Cleaning Type Reactor” (N-SCR) (tradename), each manufactured andsold by Mitsubishi Heavy Industries, Ltd., Japan; “HitachiSpectacle-Shaped Blade Processor for High-Viscosity Liquids” (tradename)and “Lattice Blade Type Polymerizer” (tradename), both manufactured andsold by Hitachi, Ltd., Japan; “BIVOLAK” (tradename), manufactured andsold by Sumitomo Heavy Industries, Ltd., Japan; and “KRC Kneader”(tradename) manufactured and sold by Kurimoto Ltd., Japan.

With respect to a free-fall polymerizer having a perforated plate,reference can be made to, for example, U.S. Pat. No. 5,596,067.

With respect to a guide-wetting fall polymerizer, reference can be madeto, for example, U.S. Pat. Nos. 5,589,564, 5,840,826, 6,265,526 and6,320,015.

In the method of the present invention, it is preferred that thepolycondensation reaction is performed using at least one reactorselected from the group consisting of a vertical agitation type reactorvessel and a surface-renewal agitation type reactor vessel. When anadditional polycondensation is performed after step (C) of the method ofthe present invention, it is preferred that the additionalpolycondensation is performed using at least one reactor selected fromthe group consisting of a vertical agitation type reactor vessel, asurface-renewal agitation type reactor vessel, a surface-renewal typetwin-screw kneading reactor, a wall-wetting fall reactor, a free-fallpolymerizer having a perforated plate, and a guide-wetting fallpolymerizer having a perforated plate and at least one guide provided inassociation with the perforated plate.

When an additional melt polycondensation is performed after step (C) ofthe method of the present invention, it is more preferred that themolten glycolic acid copolymer is treated with an inert gas to therebycause the molten glycolic acid copolymer to absorb the inert gas, andthe resultant molten glycolic acid copolymer is subjected to furtherpolycondensation reaction under reduced pressure. Differing from thecase of a molten glycolic acid copolymer not having an inert gasabsorbed therein, when a molten glycolic acid copolymer having an inertgas absorbed therein is subjected to polycondensation, vigorous foamingof the molten glycolic acid copolymer occurs, thereby improving thedegree of agitation at the surface and inner portions of the moltenglycolic acid copolymer. Accordingly, the polycondensation rate of theglycolic acid copolymer becomes increased.

Specific examples of inert gases absorbed into the molten glycolic acidcopolymer include nitrogen gas, helium gas, neon gas, argon gas, kryptongas, xenon gas, carbon dioxide gas and a gaseous saturated C₁-C₄ lowerhydrocarbon. Nitrogen gas is preferred. These gases can be usedindividually or in combination.

The glycolic acid copolymer obtained after steps (A) to (C) of themethod of the present invention or after an additional polycondensationperformed subsequent to step (C) may be granulated.

There is no particular limitation with respect to the method forgranulating the glycolic acid copolymer. For example, there can bementioned a method in which a molten glycolic acid copolymer issolidified under an atmosphere of at least one gas selected from thegroup consisting of air and inert gases, such as nitrogen gas, heliumgas, neon gas, argon gas, krypton gas, xenon gas, carbon dioxide gas anda gaseous saturated C₁-C₄ lower hydrocarbon, to thereby obtain a bulk orstrand of the glycolic acid copolymer, and the obtained bulk or strandof the glycolic acid copolymer is pulverized or cut into pieces toobtain a granulated or pelletized glycolic acid copolymer; a method inwhich a molten glycolic acid copolymer is contacted with a liquid (suchas water) to granulate or pelletize the glycolic acid copolymer; amethod in which a molten glycolic acid copolymer is contacted with aliquid (such as water) to thereby obtain a bulk of the glycolic acidcopolymer, and the obtained bulk of the glycolic acid copolymer ispulverized to obtain a granulated glycolic acid copolymer; and a methodin which a molten glycolic acid copolymer is transferred into anextruder, followed by extrusion and pelletization of the glycolic acidcopolymer. There is no particular limitation with respect to the methodfor contacting a molten glycolic acid copolymer with a liquid (such aswater) and, for example, spherical pellets can be obtained by dropwiseadding a molten glycolic acid copolymer to water, thereby solidifyingthe glycolic acid copolymer.

There is no particular limitation with respect to the shape of thegranulated or pelletized glycolic acid copolymer and, in general, theglycolic acid copolymer may be in the form of a powder, a granule, achip, a sphere, a cylinder, a tablet or a marble. There is no particularlimitation with respect to the particle diameter of the glycolic acidcopolymer. In general, the smaller the particle diameter of a solidpolymer, the larger the surface area of the solid polymer, and thus, asmaller particle diameter is advantageous from the viewpoint offacilitating the polymerization reaction. However, the handlingproperties of the particulate glycolic acid copolymer decrease with thedecrease in the particle diameter thereof. Therefore, the particlediameter of the particulate glycolic acid copolymer is generally in therange of from 10 μm to 20 mm, preferably from 0.1 mm to 10 mm.

When the glycolic acid copolymer is granulated by contacting a moltenglycolic acid copolymer with a liquid (such as water), the granulatedglycolic acid copolymer may be dried by a conventional method aftergranulation.

When the glycolic acid copolymer obtained by the method of the presentinvention is a crystallizable polymer, it is preferred that the glycolicacid copolymer is subjected to a crystallization treatment and, then, asolid phase polymerization, wherein the crystallization treatment is onemember selected from the group consisting of the following cases (i),(ii) and (iii): (i) a crystallization treatment which is performed afterthe granulation of the glycolic acid copolymer, (ii) a crystallizationtreatment which is performed before the granulation of the glycolic acidcopolymer, and (iii) a crystallization treatment which is performedsimultaneously with the granulation of the glycolic acid copolymer.

For imparting excellent crystallizability to the glycolic acidcopolymer, it is preferred that the glycolic acid copolymer which issubjected to the solid phase polymerization contains at least 82% bymole, more advantageously at least 83% by mole, most advantageously atleast 85% by mole of the glycolic acid monomer units (a), based on thetotal molar amount of the above-mentioned monomer units (a), (b) and(c).

There is no particular limitation with respect to the method forsubjecting a granulated glycolic acid copolymer to a crystallizationtreatment, and the crystallization treatment may be performed by aconventional method. For example, there can be mentioned a method inwhich the glycolic acid copolymer is crystallized by heating whilemechanically stirring and/or flowing the glycolic acid copolymer; and amethod in which the glycolic acid copolymer is crystallized by heatingwhile stirring and/or flowing the glycolic acid copolymer using theforce of a gas flow. In the above-mentioned methods, the heating of theglycolic acid copolymer is performed under an atmosphere of or under aflow of at least one gas selected from the group consisting of air andinert gases (such as nitrogen gas, helium gas, neon gas, argon gas,krypton gas, xenon gas, carbon dioxide gas and a gaseous saturated C₁-C₄lower hydrocarbon), or under reduced or superatmospheric pressure, andthe atmospheric conditions may be used in combination or varied duringthe crystallization treatment. Alternatively, the crystallizationtreatment may be performed by contacting, under heating, a solidglycolic acid copolymer with a liquid (such as water, an alcohol, analiphatic hydrocarbon, an aromatic hydrocarbon, a ketone, an ether or anester) which is incapable of dissolving the glycolic acid copolymer atthe temperature employed for the crystallization treatment.

Further, examples of modes of the crystallization treatment include amode in which the crystallization treatment is performed while allowingthe glycolic acid copolymer to stand still; a mode in which thecrystallization treatment is performed while mechanically agitating theglycolic acid copolymer (e.g., by using an impeller); a mode in whichthe crystallization treatment is performed in a vertical, horizontal orslanted vessel or a crystallization tower while rotating or vibratingthe vessel or tower to thereby agitate the glycolic acid copolymer; amode in which the crystallization treatment is performed whiletransferring the glycolic acid copolymer from an upper to a lowerposition of or from a lower to an upper position of the inside of avertical, horizontal or slanted vessel or a crystallization tower; and amode in which the glycolic acid copolymer is flowed by the force of agas flow.

The temperature of the crystallization treatment depends on the types ofthe comonomers and the composition of the glycolic acid copolymer, butthe temperature is in the range of from the glass transition temperatureof the glycolic acid copolymer to 220° C. The length of the time of thecrystallization treatment may be chosen arbitrarily, but it is generally0.5 minute to 10 hours, preferably 1 minute to 8 hours, more preferably5 minutes to 6 hours. The crystallization treatment may be performed ina batchwise manner and/or a continuous manner. Alternatively, thecrystallization treatment may be performed in several stages.

Hereinafter, in the present specification, a glycolic acid copolymerobtained after the crystallization treatment is referred to as a“crystallized glycolic acid copolymer”.

From the viewpoint of obtaining a glycolic acid copolymer having theexcellent properties of the present invention, the weight averagemolecular weight of the crystallized glycolic acid copolymer before thesolid phase polymerization is in the range of from 10,000 to 500,000.For stably producing a high molecular weight glycolic acid copolymerhaving satisfactory mechanical strength at a high polymerization rate,it is preferred that the weight average molecular weight of thecrystallized glycolic acid copolymer before the solid phasepolymerization is in the range of from 25,000 to 300,000, moreadvantageously from 30,000 to 200,000, most advantageously from 40,000to 150,000. When the weight average molecular weight exceeds 500,000,the production of such glycolic acid copolymer by the meltpolycondensation takes a long time and the discoloration of the glycolicacid copolymer is likely to occur.

The solid phase polymerization may be performed under a flow of an inertgas, or under reduced pressure or superatmospheric pressure.Alternatively, these conditions may be used in combination. Since it isnecessary to remove water by-produced during the polymerizationreaction, the solid phase polymerization is preferably performed under aflow of an inert gas and/or under reduced pressure. When the solid phasepolymerization is performed under a flow of an inert gas, there can beused at least one inert gas selected from the group consisting ofnitrogen gas, helium gas, neon gas, argon gas, krypton gas, xenon gas,carbon dioxide gas and a gaseous saturated C₁-C₄ lower hydrocarbon. Itis preferred that the gas flowed through the reaction system is a gashaving a water content as low as possible, namely a substantiallyanhydrous, dried gas. Such a dried gas can be obtained by, for example,a method in which a gas is passed through a packed bed comprised of amolecular sieve or an ion exchange resin, or a method in which a gas isdehydrated by cooling it to a low temperature. It is preferred that thewater content of the flowed gas, which is expressed in terms of a dewpoint, is −10° C. or less, more advantageously −40° C. or less.

The amount of the gas flowed through the reaction system may be selectedby taking into consideration the form, particle diameter andcrystallinity of the crystallized glycolic acid copolymer, the reactiontemperature and the vacuum level of the polymerization reaction system,and the gas is flowed through the reaction system in an amount which iscapable of removing the by-produced water to an extent which issufficient for producing a glycolic acid copolymer having satisfactorilyhigh weight average molecular weight. In general, the efficiency ofwater removal increases with the increase in the amount of gas flowedthrough the reaction system and, generally, the amount of gas used per gof a crystallized prepolymer (glycolic acid copolymer) is 0.0005 ml/minto 3,000 ml/min, preferably 0.001 ml/min to 2,500 ml/min, morepreferably 0.0015 ml/min to 2,000 ml/min, most preferably 0.002 ml/minto 500 ml/min, in terms of the volume of the gas measured underatmospheric pressure.

When the solid phase polymerization is performed under reduced pressure,there is no particular limitation with respect to the vacuum level ofthe reaction system as long as the progress of the solid phasepolymerization is maintained and a glycolic acid copolymer havingsatisfactorily high weight average molecular weight is obtained. Fromthe viewpoint of obtaining the desired levels of the polymerization rateand the weight average molecular weight of the final glycolic acidcopolymer, it is preferred that the pressure of the reaction system isin the range of from 13.3 Pa to 1.33×10³ Pa. When the solid phasepolymerization is performed under superatmospheric pressure, there is noparticular limitation with respect to the pressure of the reactionsystem as long as the progress of the solid phase polymerization ismaintained and a glycolic acid copolymer having satisfactorily highweight average molecular weight is obtained. For example, it ispreferred that the reaction is performed under a pressure in the rangeof from above atmospheric pressure to 1 MPa, more advantageously fromabove atmospheric pressure to 0.5 MPa.

There is no particular limitation with respect to the reactiontemperature for the solid phase polymerization as long as thecrystallized glycolic acid copolymer maintains a substantially solidstate in the reaction system. From the viewpoint of obtaining thedesired level of the polymerization rate, the reaction temperature ispreferably in the range of from 100° C. to the melting temperature ofthe crystallized glycolic acid copolymer, more preferably from 120° C.to 5° C. below the melting temperature of the crystallized glycolic acidcopolymer, most preferably from 140° C. to 10° C. below the meltingtemperature of the crystallized glycolic acid copolymer. The reactiontemperature may vary during the solid phase polymerization as long asthe temperature falls within the above mentioned range.

During the solid phase polymerization, the melting temperature of thecrystallized glycolic acid copolymer may become increased by theincrease in the molecular weight of the glycolic acid copolymer or bythe effect of annealing. In such case, the reaction temperature may beincreased in accordance with the increase in the melting temperature ofthe crystallized glycolic acid copolymer.

The solid phase polymerization may be performed using at least onereactor selected from the group consisting of a batch reactor and acontinuous reactor.

There is no particular limitation with respect to the reactor used forthe solid phase polymerization and there can be used a conventionaldrying apparatus, for example, a co-flow band dryer, a tunnel dryer, anaerated band dryer, a forced air dryer, an aerated vertical (movablephase) dryer, a cylindrical and hollow wedge-shaped agitating dryer, amixing dryer, a disc dryer, a rotary dryer, an aerated rotary dryer, afluidized bed dryer, a cone rotary dryer, a spray dryer, an air dryer, amulti-cylindrical dryer, a Hopper type dryer and the like described in“Kagaku Kougaku Benran (Chemical Engineering Handbook)” 5th edition, 5thprint, p. 673-691 (published by MARUZEN CO., LTD., Japan, 1995).

The weight average molecular weight of the glycolic acid copolymer afterthe solid phase polymerization is generally 1,000,000 or less.

The polycondensation process comprising the steps (A), (B) and (C) ofthe method of the present invention, as well as the additional meltpolycondensation and the solid phase polymerization which are performedafter the polycondensation process, may be performed either in acontinuous manner or an intermittent manner.

If desired, after the polycondensation reaction, the glycolic acidcopolymer obtained by the method of the present invention may be reactedwith an acid anhydride (such as acetic anhydride), an epoxy compound andthe like to thereby modify the polymer terminals.

There is no particular limitation with respect to the material used forproducing the polycondensation reactor used in the present invention. Ingeneral, by taking the corrosion resistance and the like intoconsideration, the material used for producing the polycondensationreactor is selected from glass, stainless steel, carbon steel, nickel,Hastelloy, titanium, chromium, zirconium, other alloys and polymermaterials having high heat resistance. If desired, the surface of thepolycondensation rector may be subjected to a surface treatment, such asplating, lining, passivation, washing with an acid or washing with analkali.

In addition, depending on the use and desired properties of the glycolicacid copolymer, additives, such as a phenol type antioxidant, athioether type antioxidant, a UV inhibitor, a hindered amine type lightstabilizer, an aliphatic metal salt (such as calcium stearate), anucleating agent and a plasticizer, may be added to the glycolic acidcopolymer. The amount of the additive used is generally 0.0005 to 40% byweight, preferably 0.001 to 30% by weight, based on the weight of theglycolic acid copolymer.

The glycolic acid copolymer obtained by the method of the presentinvention may be melted and shaped into articles (such as variouscontainers), a stretched or non-stretched film or sheet, a foamedarticle, a fiber and the like. If desired, the glycolic acid copolymermay be subjected to heat treatment after shaping.

Specific examples of shaped articles include bottles for drinks,cosmetics or detergents; disposable containers, such as cups and trays;casings for heat insulating boxes and various cartridges; plant pots andseedbeds for agricultural applications; construction and civilengineering materials, such as buried pipes free from the need ofrecovery, a temporary tacking material and a block; stationeries, suchas a ball point pen, a mechanical pencil and a pencil; and equipments,such as a golf tee. Specific examples of films and sheets include a filmfor agricultural uses, a shopping bag, a packaging film, a wrappingfilm, various tapes, and a bag for storing a fertilizer. Specificexamples of foamed articles include a tray for foods, a cushioningmaterial and a heat insulating material. Specific examples of fibersinclude a fishing line, a fishing net, a non-woven fabric and a suture.As special applications of the glycolic acid copolymer, there can bementioned various compositions, such as a slow-acting fertilizercomposition obtained by blending the glycolic acid copolymer into afertilizer, and various capsules for agrichemicals and fertilizers.

If desired, the obtained shaped articles may be subjected to varioussurface treatments, such as a coating treatment and a corona dischargetreatment, for improving the antistatic properties or foggingresistance. Further, various laminations, other coating treatments,aluminum deposition in vacuo and the like may be performed to improve,e.g., the sealing properties, moisture barrier properties, gas barrierproperties and printing properties of the shaped articles.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the present invention will be described in more detail withreference to the following Examples, Comparative Examples and ReferenceExamples, which should not be construed as limiting the scope of thepresent invention.

In the following Examples, Comparative Examples and Reference Examples,various measurements were performed by the following methods.

(1) Amounts of Monomer Units Constituting a Glycolic Acid Copolymer

(1-1) Amount of diglycolic acid monomer units is measured by a highperformance liquid chromatography (HPLC) apparatus under the followingconditions.

A mass of a glycolic acid copolymer is pulverized, followed by drying at80° C. under a pressure of 1×10² Pa for 6 hours, thereby obtaining adried resin. 5 g of the obtained dried resin is weighed and, then,hydrolyzed in 20 ml of an 8 N aqueous NaOH solution at room temperaturefor 48 hours. To the resultant hydrolysis product is added 12.5 ml of aconcentrated hydrochloric acid to thereby obtain an acidified aqueoussolution. The obtained acidified aqueous solution is used as a samplesolution.

With respect to the sample solution, HPLC is performed using a 0.75% byweight aqueous phosphoric acid solution as an eluent under conditionswherein the column temperature is 40° C. and the flow rate of the eluentis 1 ml/minute. In the HPLC, the sample solution is flowed through 2columns (RSpak (tradename) KC-811, manufactured and sold by Showa DenkoK.K., Japan) which are connected in series, and the absorbance of a peakascribed to diglycolic acid, which is detected by a UV detector(wavelength: 210 nm), is measured.

The amount of diglycolic acid monomer units present in a glycolic acidcopolymer is expressed in terms of the molar amount of diglycolic acidmonomer units contained in 1 g of the dried resin, wherein the molaramount is calculated from the amount of diglycolic acid monomer unitspresent in the weighed dried resin (5 g), using a calibration curve ofdiglycolic acid which has been separately prepared.

(1-2) Amount of Monomer Units Other than Diglycolic Acid Monomer Units,Which are Present in a Glycolic Acid Copolymer

Deuterated hexafluoroisopropanol as a solvent is added to a glycolicacid copolymer which has been dried at 80° C. under a pressure of 1×10²Pa for 6 hours (deuterated hexafluoroisopropanol:glycolic acid copolymerratio=1 (ml): 30 (mg)), thereby obtaining a solution of a glycolic acidcopolymer in deuterated hexafluoroisopropanol. To the obtained solutionis added tetramethylsilane as a standard substance in a very smallamount, thereby obtaining a test sample. With respect to the obtainedtest sample, 1H-NMR (400 MHz) is performed by α-400 (manufactured andsold by JASCO Corporation, Japan) wherein the number of integration is500 times. From the results of the ¹H-NMR, the amount of monomer unitsother than diglycolic acid monomer units is calculated in terms of amolar ratio thereof to the total of monomer units constituting theglycolic acid copolymer.

Subsequently, from the molar amount of diglycolic acid monomer unitscontained in 1 g of a glycolic acid copolymer which is calculated initem (1-1) above and the molar ratio of monomer units other thandiglycolic acid monomer units which is calculated in item (1-2) above,the respective contents (mol %) of the monomer units constituting 1 g ofthe dried resin are calculated using the formula weights of themonomers. In the calculation, the terminal structures of the copolymerare ignored since the molecular weight of the copolymer of the presentinvention is satisfactorily high. That is, the calculation is carriedout on the assumption that the glycolic acid copolymer is comprised onlyof monomer units corresponding to the raw material compounds.

The above-mentioned calculation method is generally employed in the art.A specific example of the calculation method is mentioned below.

The calculation of the amounts of the monomer units constituting aglycolic acid copolymer is carried out on the assumption that a glycolicacid copolymer (Y) is comprised only of glycolic acid monomer units;monomer units derived from a single type of non-glycolic,hydroxycarboxylic acid; diglycolic acid monomer units; and monomer unitsderived from a single type of polyol, wherein the formula weights of theglycolic acid monomer units, the non-glycolic, hydroxycarboxylic acidmonomer units, the diglycolic acid monomer units and the polyol monomerunits are designated as α1, β1, γ1 and δ1, respectively.

Further, the content (mole) of the diglycolic acid monomer units whichis calculated in item (1-1) above is designated as M01, and the molarratio of the glycolic acid monomer units, the molar ratio of thenon-glycolic, hydroxycarboxylic acid monomer units and the molar ratioof the polyol monomer units are designated as M1, M2 and M3,respectively.

The weight (Z) (g) of monomer units other than diglycolic acid monomerunits, which are contained in 1 g of glycolic acid copolymer (Y), isrepresented by the following formula:Z=1−γ1×M01.

The average formula weight (MA) of the monomer units other thandiglycolic acid monomer units is represented by the following formula:MA=(α1×M1+β1×M2+δ1×M3)/(M1+M2+M3).

Accordingly, with respect to the molar amounts of monomer units otherthan diglycolic acid monomer units, the molar amount (M11) of theglycolic acid monomer units, the molar amount (M21) of the non-glycolic,hydroxycarboxylic acid monomer units and the molar amount (M31) of thepolyol monomer units are respectively represented by the followingformulae:M11=(Z/MA)×M1/(M1+M2+M3),M21=(Z/MA)×M2/(M1+M2+M3) andM31=(Z/MA)×M3/(M1+M2+M3).

The thus calculated M11, M21, M01 and M31 are, respectively, the molaramount of the glycolic acid monomer units, the molar amount of thenon-glycolic, hydroxycarboxylic acid monomer units, the molar amount ofthe diglycolic acid monomer units and the molar amount of the polyolmonomer units, which are contained in 1 g of a glycolic acid copolymer.These values are used in the calculation of the contents of the monomerunits constituting the glycolic acid copolymer.

(2) Average Chain Length of a Plurality of Segments, each Constituted ByNon-Glycolic, Hydroxycarboxylic Acid Monomer Unit(s)

1 ml of deuterated hexafluoroisopropanol as a solvent is added to 30 mgof a glycolic acid copolymer which has been dried at 80° C. under apressure of 1×10² Pa for 6 hours, thereby obtaining a glycolic acidcopolymer solution in deuterated hexafluoroisopropanol. To the obtainedsolution is added tetramethylsilane as a standard substance in a verysmall amount, thereby obtaining a test sample. With respect to theobtained test sample, ¹³C-NMR is performed by α-400 (manufactured andsold by JASCO Corporation, Japan) wherein protons are completelydecoupled and the number of integration is 10,000 times.

The average chain length (γ) of a plurality of segments, eachconstituted of the non-glycolic, hydroxycarboxylic acid monomer unit(s),is calculated using the following values: an integrated intensity (α) ofa peak ascribed to a carbonyl group formed between two adjacentnon-glycolic, hydroxycarboxylic acid monomer units; and sum (β) of anintegrated intensity of a peak ascribed to a carbonyl group formedbetween a non-glycolic, hydroxycarboxylic acid monomer unit and aglycolic acid monomer unit which are adjacent to each other and anintegrated intensity of a peak ascribed to a carbonyl group formedbetween a non-glycolic, hydroxycarboxylic acid monomer unit and amonomer unit other than a non-glycolic, hydroxycarboxylic acid monomerunit which are adjacent to each other. Specifically, the average chainlength (γ) is calculated by the following formula (9):γ=α/β+1  (9).

(3) Weight Average Molecular Weight of a Glycolic Acid Copolymer

The weight average molecular weight of a glycolic acid copolymer ismeasured by a gel permeation chromatography (GPC) apparatus (8020GPCsystem, manufactured and sold by TOSOH Corporation, Japan) under thefollowing conditions.

As a solvent for the GPC, an 80 mM sodium trifluoroacetate (reagent,manufactured and sold by Wako Pure Chemical Industries, Ltd., Japan) inhexafluoroisopropanol is prepared. Specifically, 6.48 g of sodiumtrifluoroacetate is dissolved in 1,000 g of hexafluoroisopropanol toprepare a solution (hereinafter referred to simply as “eluent”).

20 mg of a glycolic acid copolymer which has been dried at 80° C. undera pressure of 1×10² Pa for 6 hours is weighed and, then, dissolved in 3g of the above-mentioned eluent, followed by filtration using a filterhaving a mesh size of 2 pin, thereby obtaining a sample solution.

With respect to the sample solution, GPC is performed under conditionswherein the column temperature is 40° C. and the flow rate of the eluentis 1 ml/minute. In the GPC, the sample solution is flowed through threedifferent columns (TskguardcolumnHHR-H (tradename) as a guard column;and Tskgel (tradename) G5000HHR and Tskgel (tradename) G3000HHR, each ofwhich is manufactured and sold by TOSOH Corporation, Japan) which areconnected in series. A calibration curve is obtained in advance from theelution times of standard monodisperse polymethyl methacrylate samples(which, respectively, have known weight average molecular weights of1,577,000, 685,000, 333,000, 100,250, 62,600, 24,300, 12,700, 4,700,1,680 and 1,140) (manufactured and sold by Polymer Laboratories Ltd,U.K.) and a methyl methacrylate monomer (molecular weight: 100), whichelution times are determined by an RI detector. The molecular weight ofa glycolic acid copolymer is calculated using the calibration curve andthe elution time of the sample solution.

(4) Melting Temperature of a Glycolic Acid Copolymer

The melting temperature of a glycolic acid copolymer is determined inaccordance with JIS K7121.

Specifically, the melting temperature of a glycolic acid copolymer isdetermined from a DSC curve obtained using DSC-7 (manufactured and soldby Perkin Elmer, Inc., U.S.A.). The DSC curve is obtained by elevatingthe temperature of the glycolic acid copolymer, which has been dried at80° C. under a pressure of 1×10² Pa for 6 hours, from −20° C. to 250° C.at a rate of 10° C./minute. When multiple peaks are observed in theobtained DSC curve, the highest of the temperatures at which peaks areobserved is defined as the melting temperature.

(5) Melt Heat Stability of a Glycolic Acid Copolymer

7.5 g of a glycolic acid copolymer is introduced into a flask having animpeller. Then, the inside of the flask is purged with dry nitrogen atroom temperature, followed by drying in vacuo (1×10² Pa) at 80° C. for 6hours while gently stirring. After completion of drying, the pressure inthe flask is adjusted with dry nitrogen to atmospheric pressure. Then,the temperature of the glycolic acid copolymer is elevated to 240° C.while stirring, to thereby melt the glycolic acid copolymer. 5 Minutesafter the time at which the temperature of the copolymer reaches 235°C., a sample of the copolymer is taken from the flask. The degree ofdiscoloration of the sampled glycolic acid copolymer is evaluated asfollows. The color tone is used as a yardstick for the melt heatstability of the glycolic acid copolymer.

(Evaluation of the Degree of Discoloration of the Glycolic AcidCopolymer)

Gel permeation chromatography (GPC) is performed in substantially thesame manner as in item (3) above (measurement of the weight averagemolecular weight of the glycolic acid copolymer) except that a UVdetector (UV8020, manufactured and sold by TOSOH Corporation, Japan) isused as a detector, wherein the wavelength is set at 350 nm. The countobtained by the UV detector is defined as a degree of discoloration.

The smaller the count (degree of discoloration), the better the colortone of the glycolic acid copolymer, that is, the higher the melt heatstability of the glycolic acid copolymer. The count numbers obtained bythe UV detector correspond to the visually observed color tones of thecopolymer as follows.

When the count (degree of discoloration) is less than 50, the glycolicacid copolymer is white or pale yellow. When the count is 50 to 100, theglycolic acid copolymer is yellow. When the count is more than 100, theglycolic acid copolymer is brown or dark brown.

(6) Evaluation of the Gas Barrier Property of a Melt-Shaped Sheet of theGlycolic Acid Copolymer

(Production of a Melt-Shaped Sheet of the Glycolic Acid Copolymer)

The glycolic acid copolymer is dried in a nitrogen-circulatingthermostat dryer having a temperature of 130° C. until the water contentof the copolymer becomes 200 ppm or less, namely, for about 2 hours.Then, the resultant dried glycolic acid copolymer is heated and pressedby a heat presser having a temperature of 240° C. for 5 minutes,followed by cooling by a cold presser having a temperature of 25° C.,thereby obtaining a melt-shaped sheet having a thickness of 200 μm.

(Evaluation of the Gas Barrier Property)

The gas barrier property of the glycolic acid copolymer is evaluated bymeasuring the oxygen gas permeability of the melt-shaped sheet as a testsample.

The measurement of the oxygen gas permeability of the glycolic acidcopolymer is performed using an oxygen permeability measuring apparatus(OX-TRAN200H; manufactured and sold by MOCON, INC., U.S.A.) inaccordance with JIS K7126B. Specifically, the measurement is performedas follows. From the above-obtained melt-shaped sheet having a thicknessof 200 μm is cut out a square sample having a size of 120 mm×120 mm. Themeasurement is performed under conditions wherein the temperature is 23°C. and the relative humidity is 65%. From the oxygen gas permeabilityvalue at the time when the oxygen gas permeability of the sample reachesequilibrium, the oxygen gas permeability of a sheet having a thicknessof 10 μm is calculated and the obtained value (cc/m²·day·atm) is definedas the oxygen gas permeability of the glycolic acid copolymer.

The smaller the value of the oxygen gas permeability, the higher the gasbarrier property.

When the gas permeability is 10 or less, the gas barrier property isexcellent. When the gas permeability is more than 10, but not more than20, the gas barrier property is good. When the gas permeability is morethan 20, the gas barrier property is poor.

(7) Evaluation of Mechanical Properties of a Melt-Shaped Sheet of theGlycolic Acid Copolymer

(Production of a Melt-Shaped Sheet)

The glycolic acid copolymer is dried in a nitrogen-circulatingthermostat dryer having a temperature of 130° C. until the water contentof the copolymer becomes 200 ppm or less, namely, for about 2 hours.Then, the resultant dried glycolic acid copolymer is heated and pressedby a heat presser having a temperature of 240° C. for 5 minutes,followed by cooling by a cold presser having a temperature of 25° C.,thereby obtaining a melt-shaped sheet having a thickness of 200 μm.

(Evaluation of the Strength of the Melt-Shaped Sheet)

From the melt-shaped sheet (having a thickness of 200 μm) obtained aboveis cut out a square sample having a size of 100 mm×100 mm. The strengthof the square sample is evaluated under conditions wherein thetemperature is 23° C. and the relative humidity is 65%. Specifically,the evaluation is carried out as follows.

Two opposite side portions (each having a length of 100 mm and a widthof 10 mm) of the 100 mm×100 mm square sample are respectively held bymetal jigs. The square sample is then bent at an angle of 90° about acenterline extending between the middle points of the other two oppositesides of the square sample which are not held by the jigs. This bendingoperation is repeated up to 5 times, and the frequency of the bendingoperation carried out until the sample is broken is defined as thestrength of the melt-shaped sheet. In each of the case where the sampleis broken in the 5th bending operation and the case where the sample isnot broken even in the 5th operation, the strength of the sample isevaluated as “5 or more”.

When the strength of the melt-shaped sheet is “3” or less, it means thatthe sheet does not have the strength required of shaped articles, suchas a container, a film and the like. On the other hand, when thestrength is “4” or more, it means that the sheet has the strengthrequired of shaped articles, such as a container, a film and the like.

(8) Evaluation of the Biodegradability of the Melt-Shaped Sheet in Soil

The biodegradability can be determined by an evaluation in soil. Theevaluation of biodegradability in soil is carried out as follows.

A strip specimen having a size of 30 mm×100 mm is cut out from themelt-shaped sheet produced in item (7) “(Production of a melt-shapedsheet)” above. The strip specimen is then buried in the soil of afarmland at a depth of about 10 cm. The strip specimen is dug out everythree months to observe the shape of the specimen until the deformationof the strip specimen is observed. When the deformation of the stripspecimen starts within 12 months from the start of the test, the stripspecimen is evaluated as biodegradable in soil.

EXAMPLE 1

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

332 g of a 70% by weight aqueous glycolic acid solution (having adiglycolic acid content of 0.005% by mole or less, based on the molaramount of glycolic acid), 58 g of a 90% by weight aqueous L-lactic acidsolution and tetraisopropoxy germanium in an amount of 0.05% by weight,based on the total weight of the above-mentioned aqueous solutions (theamount of germanium atom was 2.2×10⁻⁶ mole per g of the monomers), wereintroduced into a 350 ml pyrex glass separable flask having adistillation tube, a plane blade paddle and a baffle plate, to obtain araw material mixture. The separable flask was then purged with nitrogen.

The molar ratio of diglycolic acid in the obtained raw material mixturewas less than 0.00005, so that the calculated molar ratio of diglycolicacid was 0. Therefore, the calculated molar ratios of glycolic acid andlactic acid were 0.84 and 0.16, respectively.

Subsequently, the separable flask was immersed in an oil bath preheatedto 150° C. and, then, stirring of the raw material mixture was performedat a revolution rate of 200 rpm for 1.5 hours under a stream ofnitrogen, thereby effecting a dehydration. Then, a polycondensationreaction was performed under conditions wherein the oil bath temperaturewas maintained at 150° C., and the pressure/time conditions weresequentially changed as follows: 5.0×10⁴ Pa for 1 hour, 2.5×10⁴ Pa for0.5 hour, 1.0×10⁴ Pa for 50 minutes, 5.0×10³ Pa for 50 minutes and2.0×10³ Pa for 50 minutes, to thereby obtain a glycolic acid copolymer.During the reaction, the temperature of the reaction mixture graduallyelevated; however, the temperature of the reaction mixture became almostconstant at 146° C. after the reaction pressure was changed to 1.0×10⁴Pa. Thus, step (A) was completed. A small portion of the glycolic acidcopolymer obtained in step (A) above was sampled and subjected tomeasurement of the molecular weight. It was found that the weightaverage molecular weight of the glycolic acid copolymer was 1,900.

The reaction temperature was gradually elevated to 190° C. over 25minutes while maintaining the revolution rate and the reduced pressure(step (B)). A small portion of the glycolic acid copolymer at the pointin time at which the reaction temperature reached 190° C. was sampledand subjected to measurement of the molecular weight. It was found thatthe weight average molecular weight of the glycolic acid copolymer was2,100.

Subsequently, the reaction temperature was elevated to 200° C. over 10minutes, whereupon the revolution rate was changed to 600 rpm and thereduced pressure was changed to 4.0×10² Pa, followed by performing areaction. The reaction was continued until the total reaction time afterthe reaction temperature exceeded 190° C. became 2.5 hours, therebyobtaining a glycolic acid copolymer having a weight average molecularweight of 13,800 (step (C)). From the point in time at which thereaction temperature exceeded 190° C., it took 100 minutes for theweight average molecular weight of the glycolic acid copolymer to reach10,000. The increasing rate of the weight average molecular weightwithin this period of 100 minutes was 4,740/hour.

The glycolic acid copolymer obtained above in the molten state wascooled to obtain a solidified glycolic acid copolymer having a lowmolecular weight. Then, the obtained low molecular weight glycolic acidcopolymer was taken out of the separable flask and further polymerizedby the operations explained below.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer

25 g of the low molecular weight glycolic acid copolymer obtained abovewas introduced into a cylindrical pyrex glass tube having an innerdiameter of 70 mm and an effective length of 250 mm. The cylindricaltube containing the low molecular weight glycolic acid copolymer wasplaced in a glass tube oven (GTO-350RG, manufactured and sold by SIBATASCIENTIFIC TECHNOLOGY LTD., Japan) equipped with a planar heater. Afterthe inside of the glass tube oven was purged with nitrogen at roomtemperature, rotation of the cylindrical tube was started and thereaction temperature was elevated to 200° C. Melt polycondensation wasthen performed under a pressure of 2.6×10 Pa for 12 hours. After themelt polycondensation, the pressure in the cylindrical tube was adjustedwith dry nitrogen to atmospheric pressure, followed by cooling andsolidification of the contents (i.e., the resultant glycolic acidcopolymer) of the cylindrical tube. The obtained glycolic acid copolymerwas taken out of the cylindrical tube.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b) above was 123,000. The glycolic acid copolymer wascomprised of 83.97% by mole of glycolic acid monomer units, 0.03% bymole of diglycolic acid monomer units and 16.00% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units,wherein the lactic acid monomer units constituted a plurality ofsegments having an average chain length of 1.08 in terms of the averagenumber of lactic acid monomer units. The degree of discoloration was 28.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b) above and the properties of a melt-shaped sheet of the glycolic acidcopolymer were evaluated. It was found that the degree of discolorationof the glycolic acid copolymer after the melt heat stability test was36, which means that the melt heat stability resistance was fairly good.The oxygen gas permeability of the melt-shaped sheet of the glycolicacid copolymer was 9.1 (cc/m²·day·atm), which means that the melt-shapedsheet had extremely excellent gas barrier property. Further, thestrength of the melt-shaped sheet was 4, which means that themelt-shaped sheet had the high mechanical strength required of shapedarticles such as a container, a film and the like. The melt-shaped sheetalso had the biodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 1.

EXAMPLE 2

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 360 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 40.83 g of a 90% by weightaqueous L-lactic acid solution, and tetraisopropoxy germanium in anamount of 0.05% by weight, based on the total weight of theabove-mentioned aqueous solutions (the amount of germanium atom was2.2×10⁻⁶ mole per g of the monomers), to obtain a raw material mixture.The molar ratio of diglycolic acid in the obtained raw material mixturewas less than 0.00005, so that the calculated molar ratio of diglycolicacid was 0. Therefore, the calculated molar ratios of glycolic acid andlactic acid were 0.89 and 0.11, respectively. Except for the use ofthese operation conditions, a polycondensation reaction operation(comprised of the steps (A), (B) and (C)) was performed in substantiallythe same manner as in item (a) of Example 1, to thereby obtain aglycolic acid copolymer having a weight average molecular weight of13,800. During the reaction in step (A), the temperature of the reactionmixture gradually elevated; however, the temperature of the reactionmixture became almost constant at 146° C. after the reaction pressurewas changed to 1.0×10⁴ Pa. It was found that the weight averagemolecular weight of the glycolic acid copolymer just after completion ofstep (A) was 1,900, and that the weight average molecular weight of theglycolic acid copolymer at the point in time at which the reactiontemperature reached 190° C. was 2,100. It was also found that, from thepoint in time at which the reaction temperature exceeded 190° C., ittook 100 minutes for the weight average molecular weight of the glycolicacid copolymer to reach 10,000. The increasing rate of the weightaverage molecular weight within this period of 100 minutes was4,740/hour.

The glycolic acid copolymer obtained above in the molten state wascooled to obtain a solidified glycolic acid copolymer having a lowmolecular weight. Then, the obtained low molecular weight glycolic acidcopolymer was taken out of the separable flask and further polymerizedby the operations explained below.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by Crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

35 g of the low molecular weight glycolic acid copolymer obtained abovewas introduced into a cylindrical pyrex glass tube having an innerdiameter of 70 mm and an effective length of 250 mm. The cylindricaltube containing the low molecular weight glycolic acid copolymer wasplaced in a glass tube oven (GTO-350RG, manufactured and sold by SIBATASCIENTIFIC TECHNOLOGY LTD., Japan) equipped with a planar heater. Afterthe inside of the glass tube oven was purged with nitrogen at roomtemperature, rotation of the cylindrical tube was started and thereaction temperature was elevated to 200° C. Melt polycondensation wasthen performed under a pressure of 2.6×10 Pa for 3.5 hours. After themelt polycondensation, the pressure in the cylindrical tube was adjustedwith dry nitrogen to atmospheric pressure, followed by cooling of thecontents (i.e., the resultant glycolic acid copolymer) of thecylindrical tube to room temperature.

Subsequently, the rotation of the cylindrical tube was continued forfive hours while heating at 130° C. under dry nitrogen, therebycrystallizing the contents of the cylindrical tube, followed by coolingand solidification. The resultant crystallized glycolic acid copolymerwas taken out of the cylindrical tube. It was found that the thusobtained crystallized glycolic acid copolymer had a weight averagemolecular weight of 43,200.

The above-obtained crystallized glycolic acid copolymer was subjected topulverization, followed by sieving of the resultant, to thereby obtain apulverized, crystallized glycolic acid copolymer having a particlediameter of from 100 to 300 μm (hereinafter referred to as “crystallizedglycolic acid copolymer P-1”). It was found that the thus obtainedcrystallized glycolic acid copolymer P-1 had a melting temperature of185° C.

The crystallized glycolic acid copolymer P-1 was then subjected to solidphase polymerization as follows.

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

25 g of the pulverized, crystallized glycolic acid copolymer P-1obtained above was introduced into a cylindrical SUS 316 verticalreactor having an inner diameter of 40 mm and an effective length of 50mm. A solid phase polymerization reaction was then performed for 30hours under a pressure of 1.013×10⁵ Pa (i.e., atmospheric pressure) andunder a stream of nitrogen gas (having a dew-point temperature of −95°C. and preheated at 170° C.) at a flow rate of 30 NL/min (as measured at25° C. under atmospheric pressure).

(C) the Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 186,000. The glycolic acid copolymerwas comprised of 88.97% by mole of glycolic acid monomer units, 0.03% bymole of diglycolic acid monomer units and 11.00% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units,wherein the lactic acid monomer units constituted a plurality ofsegments having an average chain length of 1.02 in terms of the averagenumber of lactic acid monomer units. The degree of discoloration was 29.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the degree ofdiscoloration of the glycolic acid copolymer after the melt heatstability test was 38, which means that the melt heat stability wasfairly good. The oxygen gas permeability of the melt-shaped sheet of theglycolic acid copolymer was 8.0 (cc/m²·day·atm), which means that themelt-shaped sheet had extremely excellent gas barrier property. Further,the strength of the melt-shaped sheet was 5 or more, which means thatthe melt-shaped sheet had the high mechanical strength required ofshaped articles such as a container, a film and the like. Themelt-shaped sheet also had the biodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 1.

EXAMPLE 3

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 360 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 21 g of a 90% by weightaqueous L-lactic acid solution, and tetraisopropoxy germanium in anamount of 0.05% by weight, based on the total weight of theabove-mentioned aqueous solutions (the amount of germanium atom was2.3×10⁻⁶ mole per g of the monomers), to obtain a raw material mixture.The molar ratio of diglycolic acid in the obtained raw material mixturewas less than 0.00005, so that the calculated molar ratio of diglycolicacid was 0. Therefore, the calculated molar ratios of glycolic acid andlactic acid were 0.94 and 0.06, respectively. Except for the use ofthese operation conditions, a polycondensation reaction operation wasperformed in substantially the same manner as in step (A) of Example 1,to thereby obtain a glycolic acid copolymer. During the reaction in step(A), the temperature of the reaction mixture gradually elevated;however, the temperature of the reaction mixture became almost constantat 146° C. after the reaction pressure was changed to 1.0×10⁴ Pa. Asmall portion of the glycolic acid copolymer obtained in step (A) abovewas sampled and subjected to measurement of the molecular weight. It wasfound that the weight average molecular weight of the glycolic acidcopolymer was 1,900.

The reaction temperature was gradually elevated to 190° C. over 25minutes while maintaining the revolution rate and the reduced pressure(step (B)). A small portion of the glycolic acid copolymer at the pointin time at which the reaction temperature reached 190° C. was sampledand subjected to measurement of the molecular weight. It was found thatthe weight average molecular weight of the glycolic acid copolymer was2,100.

Subsequently, the reaction temperature was elevated to 225° C. over 20minutes, whereupon the revolution rate was changed to 600 rpm and thereduced pressure was changed to 4.0×10² Pa, followed by performing areaction. The reaction was continued until the total reaction time afterthe reaction temperature exceeded 190° C. became 2.5 hours, therebyobtaining a glycolic acid copolymer having a weight average molecularweight of 16,300 (step (C)). From the point in time at which thereaction temperature exceeded 190° C., it took 80 minutes for the weightaverage molecular weight of the glycolic acid copolymer to reach 10,000.The increasing rate of the weight average molecular weight within thisperiod of 80 minutes was 5,925/hour.

The glycolic acid copolymer obtained above in the molten state wascooled to obtain a solidified glycolic acid copolymer having a lowmolecular weight. Then, the obtained low molecular weight glycolic acidcopolymer was taken out of the separable flask and further polymerizedby the operations explained below.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by Crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, except thatthe reaction temperature was changed to 225° C., to thereby obtain apulverized, crystallized glycolic acid copolymer having a weight averagemolecular weight of 46,300 and a melting temperature of 209° C.(hereinafter referred to as “crystallized glycolic acid copolymer P-2”).

The crystallized glycolic acid copolymer P-2 was then subjected to solidphase polymerization as follows.

(B-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

The above-obtained crystallized glycolic acid copolymer P-2 wassubjected to solid phase polymerization reaction in substantially thesame manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 182,000. The glycolic acid copolymerwas comprised of 93.97% by mole of glycolic acid monomer units, 0.03% bymole of diglycolic acid monomer units and 6.00% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units,wherein the lactic acid monomer units constituted a plurality ofsegments having an average chain length of 1.02 in terms of the averagenumber of lactic acid monomer units. The degree of discoloration was 29.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the degree ofdiscoloration of the glycolic acid copolymer after the melt heatstability test was 43, which means that the melt heat stability wasfairly good. The oxygen gas permeability of the melt-shaped sheet of theglycolic acid copolymer was 7.2 (cc/m²·day·atm), which means that themelt-shaped sheet had extremely excellent gas barrier property. Further,the strength of the melt-shaped sheet was 5 or more, which means thatthe melt-shaped sheet had the high mechanical strength required ofshaped articles such as a container, a film and the like. Themelt-shaped sheet also had the biodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 1.

EXAMPLE 4

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 338 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 51 g of 6-hydroxyhexanoicacid, and stannous chloride in an amount of 0.03% by weight, based onthe total weight of the above-mentioned raw materials (the amount of tinatom was 2.1×10⁻⁶ mole per g of the monomers), to obtain a raw materialmixture. The molar ratio of diglycolic acid in the obtained raw materialmixture was less than 0.00005, so that the calculated molar ratio ofdiglycolic acid was 0. Therefore, the calculated molar ratios ofglycolic acid and 6-hydroxyhexanoic acid were 0.89 and 0.11,respectively. Except for the use of these operation conditions, apolycondensation reaction operation (comprised of the steps (A), (B) and(C)) was performed in substantially the same manner as in item (a) ofExample 2, to thereby obtain a glycolic acid copolymer having a weightaverage molecular weight of 13,000.

During the reaction in step (A), the temperature of the reaction mixturegradually elevated; however, the temperature of the reaction mixturebecame almost constant at 146° C. after the reaction pressure waschanged to 1.0×10⁴ Pa. It was found that the weight average molecularweight of the glycolic acid copolymer just after completion of step (A)was 1,900, and that the weight average molecular weight of the glycolicacid copolymer at the point in time at which the reaction temperaturereached 190° C. was 2,100. It was also found that, from the point intime at which the reaction temperature exceeded 190° C., it took 105minutes for the weight average molecular weight of the glycolic acidcopolymer to reach 10,000. The increasing rate of the weight averagemolecular weight within this period of 105 minutes was 4,514/hour.

The glycolic acid copolymer obtained above in the molten state wascooled to obtain a solidified glycolic acid copolymer having a lowmolecular weight. Then, the obtained low molecular weight glycolic acidcopolymer was taken out of the separable flask and further polymerizedby the operations explained below.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by Crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 42,900 and a melting temperature of183° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-3”).

The crystallized glycolic acid copolymer P-3 was then subjected to solidphase polymerization as follows.

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

The above-obtained crystallized glycolic acid copolymer P-3 wassubjected to solid phase polymerization reaction in substantially thesame manner as in item (b-2) of Example 2.

(c) The results of the analysis of the glycolic acid copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 167,000. The glycolic acid copolymerwas comprised of 88.97% by mole of glycolic acid monomer units, 0.03% bymole of diglycolic acid monomer units and 11.00% by mole of6-hydroxyhexanoic acid monomer units as non-glycolic, hydroxycarboxylicacid monomer units, wherein the 6-hydroxyhexanoic acid monomer unitsconstituted a plurality of segments having an average chain length of1.03 in terms of the average number of 6-hydroxyhexanoic acid monomerunits. The degree of discoloration was 29.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the degree ofdiscoloration of the glycolic acid copolymer after the melt heatstability test was 38, which means that the melt heat stability wasfairly good. The oxygen gas permeability of the melt-shaped sheet of theglycolic acid copolymer was 8.1 (cc/m²·day·atm), which means that themelt-shaped sheet had extremely excellent gas barrier property. Further,the strength of the melt-shaped sheet was 5 or more, which means thatthe melt-shaped sheet had the high mechanical strength required ofshaped articles such as a container, a film and the like. Themelt-shaped sheet also had the biodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 1.

EXAMPLE 5

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 338 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 30 g of 3-hydroxybutylicacid, and tetraisopropoxy germanium in an amount of 0.05% by weight,based on the total weight of the above-mentioned raw materials (theamount of germanium atom was 2.2×10⁻⁶ mole per g of the monomers), toobtain a raw material mixture. The molar ratio of diglycolic acid in theobtained raw material mixture was less than 0.00005, so that thecalculated molar ratio of diglycolic acid was 0. Therefore, thecalculated molar ratios of glycolic acid and 3-hydroxybutylic acid were0.89 and 0.11, respectively. Except for the use of these operationconditions, a polycondensation reaction operation (comprised of thesteps (A), (B) and (C)) was performed in substantially the same manneras in item (a) of Example 2, to thereby obtain a glycolic acid copolymerhaving a weight average molecular weight of 13,700.

During the reaction in step (A), the temperature of the reaction mixturegradually elevated; however, the temperature of the reaction mixturebecame almost constant at 146° C. after the reaction pressure waschanged to 1.0×10⁴ Pa. It was found that the weight average molecularweight of the glycolic acid copolymer just after completion of step (A)was 1,900, and that the weight average molecular weight of the glycolicacid copolymer at the point in time at which the reaction temperaturereached 190° C. was 2,100. It was also found that, from the point intime at which the reaction temperature exceeded 190° C., it took 100minutes for the weight average molecular weight of the glycolic acidcopolymer to reach 10,000. The increasing rate of the weight averagemolecular weight within this period of 100 minutes was 4,740/hour.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by Crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 43,000 and a melting temperature of184° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-4”).

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

Subsequently, the above-obtained crystallized glycolic acid copolymerP-4 was subjected to solid phase polymerization reaction insubstantially the same manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 179,000. The glycolic acid copolymerwas comprised of 88.97% by mole of glycolic acid monomer units, 0.03% bymole of diglycolic acid monomer units and 11.00% by mole of3-hydroxybutylic acid monomer units as non-glycolic, hydroxycarboxylicacid monomer units, wherein the 3-hydroxybutylic acid monomer unitsconstituted a plurality of segments having an average chain length of1.02 in terms of the average number of 3-hydroxybutylic acid monomerunits. The degree of discoloration was 28.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the degree ofdiscoloration of the glycolic acid copolymer after the melt heatstability test was 39, which means that the melt heat stability wasfairly good. The oxygen gas permeability of the melt-shaped sheet of theglycolic acid copolymer was 8.0 (cc/m²·day·atm), which means that themelt-shaped sheet had extremely excellent gas barrier property. Further,the strength of the melt-shaped sheet was 5 or more, which means thatthe melt-shaped sheet had the high mechanical strength required ofshaped articles such as a container, a film and the like. Themelt-shaped sheet also had the biodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 1.

COMPARATIVE EXAMPLE 1

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 360 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 40.83 g of a 90% by weightaqueous L-lactic acid solution and tetraisopropoxy germanium in anamount of 0.05% by weight, based on the total weight of theabove-mentioned aqueous solutions (the amount of germanium atom was2.2×10⁻⁶ mole per g of the monomers), to obtain a raw material mixture.The separable flask was then purged with nitrogen.

The molar ratio of diglycolic acid in the obtained raw material mixturewas less than 0.00005, so that the calculated molar ratio of diglycolicacid was 0. Therefore, the calculated molar ratios of glycolic acid andlactic acid were 0.89 and 0.11, respectively.

Subsequently, the separable flask was immersed in an oil bath preheatedto 150° C. and, then, stirring of the raw material mixture was performedat a revolution rate of 200 rpm for 1.5 hours under a stream ofnitrogen, thereby effecting a dehydration. Then, a polycondensationreaction was performed under conditions wherein the oil bath temperaturewas maintained at 150° C., and the pressure/time conditions weresequentially changed as follows: 5.0×10⁴ Pa for 1 hour, 2.5×10⁴ Pa for0.5 hour and 1.0×10⁴ Pa for 20 minutes, to thereby obtain a glycolicacid copolymer. During the reaction, the temperature of the reactionmixture gradually elevated; however, the temperature of the reactionmixture became almost constant at 146° C. after the reaction pressurewas changed to 1.0×10⁴ Pa.

A small portion of the glycolic acid copolymer obtained in the abovestep was sampled and subjected to measurement of the molecular weight.It was found that the weight average molecular weight of the glycolicacid copolymer was 400.

The reaction temperature was gradually elevated to 190° C. over 25minutes while maintaining the revolution rate and the reduced pressure.A small portion of the glycolic acid copolymer at the point in time atwhich the reaction temperature reached 190° C. was sampled and subjectedto measurement of the molecular weight. It was found that the weightaverage molecular weight of the glycolic acid copolymer was 600.

Subsequently, the reaction temperature was elevated to 200° C. over 10minutes, whereupon the revolution rate was changed to 600 rpm and thereduced pressure was changed to 4.0×10² Pa, followed by performing areaction. The reaction was continued until the total reaction time afterthe reaction temperature exceeded 190° C. became 2.5 hours, therebyobtaining a glycolic acid copolymer having a weight average molecularweight of 12,200.

From the point at which the reaction temperature exceeded −190° C., ittook 120 minutes for the weight average molecular weight of the glycolicacid copolymer to reach 10,000. The increasing rate of the weightaverage molecular weight within this period of 120 minutes was4,700/hour.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by Crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 43,800 and a melting temperature of183° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-5”)

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

The above-obtained crystallized glycolic acid copolymer P-5 wassubjected to solid phase polymerization reaction in substantially thesame manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 109,000. The glycolic acid copolymerwas comprised of 88.86% by mole of glycolic acid monomer units, 0.13% bymole of diglycolic acid monomer units and 11.01% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units,wherein the lactic acid monomer units constituted a plurality ofsegments having an average chain length of 1.02 in terms of the averagenumber of lactic acid monomer units. The degree of discoloration was 34.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the oxygen gaspermeability of the melt-shaped sheet of the glycolic acid copolymer was8.2 (cc/m²·day·atm), which means that the melt-shaped sheet hadsatisfactory gas barrier property. Further, the strength of themelt-shaped sheet was 4, which means that the melt-shaped sheet had thehigh mechanical strength required of shaped articles such as acontainer, a film and the like. The melt-shaped sheet also had thebiodegradability in soil. However, with respect to the melt heatstability, it was found that the degree of discoloration of the glycolicacid copolymer after the melt heat stability test was 175, and that theglycolic acid copolymer was discolored to assume a brown color.

The results of the analysis and the results of the evaluation are shownin Table 2.

COMPARATIVE EXAMPLE 2

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 360 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 10.2 g of a 90% by weightaqueous L-lactic acid solution and tetraisopropoxy germanium in anamount of 0.05% by weight, based on the total weight of theabove-mentioned aqueous solutions (the amount of germanium atom was2.3×10⁻⁶ mole per g of the monomers), to obtain a raw material mixture.The molar ratio of diglycolic acid in the obtained raw material mixturewas less than 0.00005, so that the calculated molar ratio of diglycolicacid was 0. Therefore, the calculated molar ratios of glycolic acid andlactic acid were 0.97 and 0.03, respectively. Except for the use ofthese operation conditions, a polycondensation reaction operation(comprised of the steps (A), (B) and (C)) was performed in substantiallythe same manner as in item (a) of Example 3, to thereby obtain aglycolic acid copolymer having a weight average molecular weight of16,300.

During the reaction in step (A), the temperature of the reaction mixturegradually elevated; however, the temperature of the reaction mixturebecame almost constant at 146° C. after the reaction pressure waschanged to 1.0×10⁴ Pa. It was found that the weight average molecularweight of the glycolic acid copolymer just after completion of step (A)was 1,900, and that the weight average molecular weight of the glycolicacid copolymer at the point in time at which the reaction temperaturereached 190° C. was 2,100. It was also found that, from the point intime at which the reaction temperature exceeded 190° C., it took 80minutes for the weight average molecular weight of the glycolic acidcopolymer to reach 10,000. The increasing rate of the weight averagemolecular weight within this period of 80 minutes was 5,925/hour.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by Crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, except thatthe reaction temperature was changed to 230° C., to thereby obtain apulverized, crystallized glycolic acid copolymer having a weight averagemolecular weight of 46,300 and a melting temperature of 225° C.(hereinafter referred to as “crystallized glycolic acid copolymer P-6”).

The crystallized glycolic acid copolymer P-6 was then subjected to solidphase polymerization as follows.

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

The above-obtained crystallized glycolic acid copolymer P-6 wassubjected to solid phase polymerization reaction in substantially thesame manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 164,000. The glycolic acid copolymerwas comprised of 96.97% by mole of glycolic acid monomer units, 0.03% bymole of diglycolic acid monomer units and 3.00% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units,wherein the lactic acid monomer units constituted a plurality ofsegments having an average chain length of 1.01 in terms of the averagenumber of lactic acid monomer units. The degree of discoloration was 33.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the oxygen gaspermeability of the melt-shaped sheet of the glycolic acid copolymer was7.0 (cc/m²·day·atm), which means that the melt-shaped sheet hadextremely excellent gas barrier property. Further, the strength of themelt-shaped sheet was 5 or more, which means that the melt-shaped sheethad the high mechanical strength required of shaped articles such as acontainer, a film and the like. The melt-shaped sheet also had thebiodegradability in soil. However, with respect to the melt heatstability, it was found that the degree of discoloration of the glycolicacid copolymer after the melt heat stability test was 115, and that theglycolic acid copolymer was discolored to assume a brown color.

The results of the analysis and the results of the evaluation are shownin Table 2.

COMPARATIVE EXAMPLE 3

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 290 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 98.5 g of a 90% by weightaqueous L-lactic acid solution and tetraisopropoxy germanium in anamount of 0.05% by weight, based on the total weight of theabove-mentioned aqueous solutions (the amount of germanium atom was2.2×10⁻⁶ mole per g of the monomers), to obtain a raw material mixture.The molar ratio of diglycolic acid in the obtained raw material mixturewas less than 0.00005, so that the calculated molar ratio of diglycolicacid was 0. Therefore, the calculated molar ratios of glycolic acid andlactic acid were 0.73 and 0.27, respectively. Except for the use ofthese operation conditions, a polycondensation reaction operation(comprised of the steps (A), (B) and (C)) was performed in substantiallythe same manner as in item (a) of Example 1, to thereby obtain aglycolic acid copolymer having a weight average molecular weight of13,800.

During the reaction in step (A), the temperature of the reaction mixturegradually elevated; however, the temperature of the reaction mixturebecame almost constant at 146° C. after the reaction pressure waschanged to 1.0×10⁴ Pa. It was found that the weight average molecularweight of the glycolic acid copolymer just after completion of step (A)was 1,900, and that the weight average molecular weight of the glycolicacid copolymer at the point in time at which the reaction temperaturereached 190° C. was 2,100. It was also found that, from the point intime at which the reaction temperature exceeded 190° C., it took 100minutes for the weight average molecular weight of the glycolic acidcopolymer to reach 10,000. The increasing rate of the weight averagemolecular weight within this period of 100 minutes was 4,740/hour.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation in substantially the same manner asin item (b) of Example 1.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b) above was 122,000. The glycolic acid copolymer wascomprised of 72.96% by mole of glycolic acid monomer units, 0.03% bymole of diglycolic acid monomer units and 27.01% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units,wherein the lactic acid monomer units constituted a plurality ofsegments having an average chain length of 1.14 in terms of the averagenumber of lactic acid monomer units. The degree of discoloration was 33.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b) above and the properties of a melt-shaped sheet of the glycolic acidcopolymer were evaluated. It was found that the degree of discolorationof the glycolic acid copolymer after the melt heat stability test was39, and the strength of the melt-shaped sheet was 4, which means thatthe melt-shaped sheet had the high mechanical strength required ofshaped articles such as a container, a film and the like. Further, themelt-shaped sheet also had the biodegradability in soil. However, withrespect to gas barrier property, it was found that the oxygen gaspermeability of the melt-shaped sheet of the glycolic acid copolymer was35 (cc/m²·day·atm), which means that the gas barrier property of themelt-shaped sheet was poor.

The results of the analysis and the results of the evaluation are shownin Table 2.

COMPARATIVE EXAMPLE 4

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Glycolic acid and lactic acid were separately subjected to apolycondensation reaction in separate reaction apparatuses, therebyobtaining two different low molecular weight polymers. The obtained twolow molecular weight polymers were mixed together, and the resultantmixture was subjected to a reaction. Specifically, the operations wereperformed as follows.

(a-1) 60 g of a 90% by weight aqueous L-lactic acid solution wasintroduced into a 100 ml pyrex glass separable flask having adistillation tube and an anchor impeller. The separable flask was thenpurged with nitrogen. Subsequently, the separable flask was immersed inan oil bath preheated to 130° C. and, then, stirring of the contents ofthe separable flask was performed at a revolution rate of 200 rpm for1.5 hours under a stream of nitrogen, thereby effecting a dehydration.Then, a polycondensation reaction was performed under conditions whereinthe oil bath temperature was maintained at 130° C., and thepressure/time conditions were sequentially changed as follows: 5.0×1 04Pa for 1 hour, 2.5×10⁴ Pa for 1 hour, 1.0×10⁴ Pa for 1 hour, 5.0×10³ Pafor 1 hour and 2.0×10³ Pa for 1 hour, to thereby obtain a poly L-lacticacid. The poly L-lactic acid obtained above was cooled to solidify thepoly L-lactic acid. The resultant solidified, amorphous poly L-lacticacid was then taken out of the separable flask. The weight averagemolecular weight of the obtained amorphous poly L-lactic acid was 1,000.

(a-2) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as initem (a) of Example 1 were introduced 360 g of a 70% by weight aqueousglycolic acid solution (having a diglycolic acid content of 0.005% bymole or less, based on the molar amount of glycolic acid) andtetraisopropoxy germanium in an amount of 0.05% by weight, based on theweight of the above-mentioned aqueous solution (the amount of germaniumatom was 2.3×10⁻⁶ mole per g of the monomer), to obtain a raw materialmixture. The separable flask was then purged with nitrogen.Subsequently, the separable flask was immersed in an oil bath preheatedto 150° C. and, then, stirring of the raw material mixture was performedat a revolution rate of 200 rpm for 1.5 hours under a stream ofnitrogen, thereby effecting a dehydration.

Then, a polycondensation reaction was performed under conditions whereinthe oil bath temperature was maintained at 150° C., and thepressure/time conditions were sequentially changed as follows: 5.0×10⁴Pa for 1 hour, 2.5×10⁴ Pa for 0.5 hour, 1.0×10⁴ Pa for 50 minutes,5.0×10³ Pa for 50 minutes and 2.0×10³ Pa for 50 minutes, to therebyobtain a polyglycolic acid. During the reaction, the temperature of thereaction mixture gradually elevated; however, the temperature of thereaction mixture became almost constant at 146° C. after the reactionpressure was changed to 1.0×10⁴ Pa. A small portion of the polyglycolicacid obtained by the above reaction was sampled and subjected tomeasurement of the molecular weight. It was found that the weightaverage molecular weight of the polyglycolic acid was 1,900.

The reaction temperature was gradually elevated to 190° C. over 20minutes while maintaining the revolution rate and the reduced pressure.A small portion of the glycolic acid polymer at the point in time atwhich the reaction temperature reached 190° C. was sampled and subjectedto measurement of the molecular weight. It was found that the weightaverage molecular weight of the polyglycolic acid was 2,100.

Subsequently, the reaction temperature was elevated to 200° C. over 10minutes, whereupon the revolution rate was changed to 450 rpm and thereduced pressure was released by nitrogen. Then, 29.4 g of poly L-lacticacid obtained in item (a-1) above was added to the separable flask undernitrogen. The pressure was then reduced again to 4.0×10² Pa, followed byperforming a reaction. The reaction was continued until the totalreaction time after the reaction temperature exceeded 190° C. became 3hours, thereby obtaining a glycolic acid copolymer having a weightaverage molecular weight of 11,000. The glycolic acid copolymer obtainedabove in the molten state was cooled to solidify the glycolic acidcopolymer. The resultant solidified glycolic acid copolymer was takenout of the separable flask and then subjected to further polymerizationby the operations explained below.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 42,600 and a melting temperature of189° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-7”).

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

The above-obtained crystallized glycolic acid copolymer P-7 wassubjected to solid phase polymerization reaction in substantially thesame manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 187,000. The glycolic acid copolymerwas comprised of 88.97% by mole of glycolic acid monomer units, 0.03% bymole of diglycolic acid monomer units and 11.00% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units,wherein the lactic acid monomer units constituted a plurality ofsegments having an average chain length of 1.62 in terms of the averagenumber of lactic acid monomer units. The degree of discoloration was 29.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the oxygen gaspermeability of the melt-shaped sheet of the glycolic acid copolymer was8.4 (cc/m²·day·atm), which means that the melt-shaped sheet hadsatisfactory gas barrier property. Further, the strength of themelt-shaped sheet was 5 or more, which means that the melt-shaped sheethad the high mechanical strength required of shaped articles such as acontainer, a film and the like. The melt-shaped sheet also had thebiodegradability in soil. However, with respect to the melt heatstability, it was found that the degree of discoloration of the glycolicacid copolymer after the melt heat stability test was 105, and that theglycolic acid copolymer was discolored to assume a brown color.

The results of the analysis and the results of the evaluation are shownin Table 2.

EXAMPLE 6

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

A polycondensation reaction operation (comprised of the steps (A), (B)and (C)) was performed in substantially the same manner as in Example 1,except for the use of the following operation conditions (I) and (II).

(I) Into substantially the same reaction apparatus (separable flask) asin Example 1 were introduced 360 g of a 70% by weight aqueous glycolicacid solution (having a diglycolic acid content of 0.005% by mole orless, based on the molar amount of glycolic acid), 40.83 g of a 90% byweight aqueous L-lactic acid solution, 0.12 g of neopentylglycol andtetraisopropoxy germanium in an amount of 0.05% by weight, based on thetotal weight of the above-mentioned raw materials (the amount ofgermanium atom was 2.2×10⁻⁶ mole per g of the monomers), to obtain a rawmaterial mixture. The molar ratio of diglycolic acid in the obtained rawmaterial mixture was less than 0.00005, so that the calculated molarratio of diglycolic acid was 0. Therefore, the calculated molar ratiosof glycolic acid, lactic acid and neopentylglycol were 0.89, 0.1097 and0.0003, respectively.

(II) In step (A), after the dehydration was performed for 1.5 hoursunder a stream of nitrogen, a polycondensation reaction was performedunder conditions wherein the oil bath temperature was maintained at 150°C., and the pressure/time conditions were sequentially changed asfollows: 5.0×10⁴ Pa for 1 hour, 2.5×10⁴ Pa for 0.5 hour, 1.0×10⁴ Pa for50 minutes, 5.0×10³ Pa for 50 minutes and 2.0×10³ Pa for 90 minutes.

Except for the use of these operation conditions (I) and (II), apolycondensation reaction operation (comprised of the steps (A), (B) and(C)) was performed in substantially the same manner as in item (a) ofExample 1, to thereby obtain a glycolic acid copolymer having a weightaverage molecular weight of 14,400.

During the reaction in step (A), the temperature of the reaction mixturegradually elevated; however, the temperature of the reaction mixturebecame almost constant at 146° C. after the reaction pressure waschanged to 1.0×10⁴ Pa. It was found that the weight average molecularweight of the glycolic acid copolymer just after completion of step (A)was 2,500, and that the weight average molecular weight of the glycolicacid copolymer at the point in time at which the reaction temperaturereached 190° C. was 2,700. It was also found that, from the point intime at which the reaction temperature exceeded 190° C., it took 90minutes for the weight average molecular weight of the glycolic acidcopolymer to reach 10,000. The increasing rate of the weight averagemolecular weight within this period of 90 minutes was 4,867/hour.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by Crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 44,200 and a melting temperature of183° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-8”).

The crystallized glycolic acid copolymer P-8 was then subjected to solidphase polymerization as follows.

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

The above-obtained crystallized glycolic acid copolymer P-8 wassubjected to solid phase polymerization reaction in substantially thesame manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 187,000. The glycolic acid copolymerwas comprised of 88.94% by mole of glycolic acid monomer units, 0.03% bymole of diglycolic acid monomer units, 10.99% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units and0.04% by mole of neopentylglycol monomer units, wherein the lactic acidmonomer units constituted a plurality of segments having an averagechain length of 1.01 in terms of the average number of lactic acidmonomer units. The degree of discoloration was 29.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the degree ofdiscoloration of the glycolic acid copolymer after the melt heatstability test was 39, which means that the melt heat stability wasfairly good. The oxygen gas permeability of the melt-shaped sheet of theglycolic acid copolymer was 8.3 (cc/m²·day·atm), which means that themelt-shaped sheet had extremely excellent gas barrier property. Further,the strength of the melt-shaped sheet was 5 or more, which means thatthe melt-shaped sheet had the high mechanical strength required ofshaped articles such as a container, a film and the like. Themelt-shaped sheet also had the biodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 3.

EXAMPLE 7

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 360 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 40.83 g of a 90% by weightaqueous L-lactic acid solution, 0.136 g of 1,6-hexanediol andtetraisopropoxy germanium in an amount of 0.05% by weight, based on thetotal weight of the above-mentioned raw materials (the amount ofgermanium atom was 2.2×10⁻⁶ mole per g of the monomers), to obtain a rawmaterial mixture. The molar ratio of diglycolic acid in the obtained rawmaterial mixture was less than 0.00005, so that the calculated molarratio of diglycolic acid was 0. Therefore, the calculated molar ratiosof glycolic acid, lactic acid and 1,6-hexanediol were 0.89, 0.1097 and0.0003, respectively. Except for the use of these operation conditions,a polycondensation reaction operation (comprised of the steps (A), (B)and (C)) was performed in substantially the same manner as in item (a)of Example 6, to thereby obtain a glycolic acid copolymer having aweight average molecular weight of 14,400.

During the reaction in step (A), the temperature of the reaction mixturegradually elevated; however, the temperature of the reaction mixturebecame almost constant at 146° C. after the reaction pressure waschanged to 1.0×10⁴ Pa. It was found that the weight average molecularweight of the glycolic acid copolymer just after completion of step (A)was 2,500, and that the weight average molecular weight of the glycolicacid copolymer at the point in time at which the reaction temperaturereached 190° C. was 2,700. It was also found that, from the point intime at which the reaction temperature exceeded 190° C., it took 90minutes for the weight average molecular weight of the glycolic acidcopolymer to reach 10,000. The increasing rate of the weight averagemolecular weight within this period of 90 minutes was 4,867/hour.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by Crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 43,800 and a melting temperature of183° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-9”)

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

Subsequently, the above-obtained crystallized glycolic acid copolymerP-9 was subjected to a solid phase polymerization reaction insubstantially the same manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 187,000. The glycolic acid copolymerwas comprised of 88.94% by mole of glycolic acid monomer units; 0.03% bymole of diglycolic acid monomer units; 10.99% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units; and0.04% by mole of 1,6-hexanediol monomer units, wherein the lactic acidmonomer units constituted a plurality of segments having an averagechain length of 1.01 in terms of the average number of lactic acidmonomer units. The degree of discoloration was 33.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the degree ofdiscoloration of the glycolic acid copolymer after the melt heatstability test was 43, which means that the melt heat stability wasfairly good. The oxygen gas permeability of the melt-shaped sheet of theglycolic acid copolymer was 8.2 (cc/m²·day·atm), which means that themelt-shaped sheet had extremely excellent gas barrier property. Further,the strength of the melt-shaped sheet was 5 or more, which means thatthe melt-shaped sheet had the high mechanical strength required ofshaped articles such as a container, a film and the like. Themelt-shaped sheet also had the biodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 3.

EXAMPLE 8

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 360 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 40.83 g of a 90% by weightaqueous L-lactic acid solution, 0.04 g of trimethylol propane andtetraisopropoxy germanium in an amount of 0.05% by weight, based on thetotal weight of the above-mentioned raw materials (the amount ofgermanium atom was 2.2×10⁻⁶ mole per g of the monomers), to obtain a rawmaterial mixture. The molar ratio of diglycolic acid in the obtained rawmaterial mixture was less than 0.00005, so that the calculated molarratio of diglycolic acid was 0. Therefore, the calculated molar ratiosof glycolic acid, lactic acid and trymethylol propane were 0.8903,0.10962 and 0.00008, respectively. Except for the use of these operationconditions, a polycondensation reaction operation (comprised of thesteps (A), (B) and (C)) was performed in substantially the same manneras in item (a) of Example 6, to thereby obtain a glycolic acid copolymerhaving a weight average molecular weight of 15,600.

During the reaction in step (A), the temperature of the reaction mixturegradually elevated; however, the temperature of the reaction mixturebecame almost constant at 146° C. after the reaction pressure waschanged to 1.0×10⁴ Pa. It was found that the weight average molecularweight of the glycolic acid copolymer just after completion of step (A)was 2,700, and that the weight average molecular weight of the glycolicacid copolymer at the point in time at which the reaction temperaturereached 190° C. was 2,900. It was also found that, from the point intime at which the reaction temperature exceeded 190° C., it took 85minutes for the weight average molecular weight of the glycolic acidcopolymer to reach 10,000. The increasing rate of the weight averagemolecular weight within this period of 85 minutes was 5,012/hour.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by Crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 46,500 and a melting temperature of184° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-10”).

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

Subsequently, the above-obtained crystallized glycolic acid copolymerP-10 was subjected to a solid phase polymerization reaction insubstantially the same manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 325,000. The glycolic acid copolymerwas comprised of 88.98% by mole of glycolic acid monomer units; 0.03% bymole of diglycolic acid monomer units; 10.98% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units; and0.01% by mole of trimethylol propane monomer units, wherein the lacticacid monomer units constituted a plurality of segments having an averagechain length of 1.01 in terms of the average number of lactic acidmonomer units. The degree of discoloration was 34.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the degree ofdiscoloration of the glycolic acid copolymer after the melt heatstability test was 44, which means that the melt heat stability wasfairly good. The oxygen gas permeability of the melt-shaped sheet of theglycolic acid copolymer was 8.3 (cc/m²·day·atm), which means that themelt-shaped sheet had extremely excellent gas barrier property. Further,the strength of the melt-shaped sheet was 5 or more, which means thatthe melt-shaped sheet had the high mechanical strength required ofshaped articles such as a container, a film and the like. Themelt-shaped sheet also had the biodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 3.

EXAMPLE 9

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 360 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 40.83 g of a 90% by weightaqueous L-lactic acid solution, 0.12 g of neopentyl glycol, 0.04 g oftrimethylol propane and tetraisopropoxy germanium in an amount of 0.05%by weight, based on the total weight of the above-mentioned rawmaterials (the amount of germanium atom was 2.2×10⁻⁶ mole per g of themonomers), to obtain a raw material mixture. The molar ratio ofdiglycolic acid in the obtained raw material mixture was less than0.00005, so that the calculated molar ratio of diglycolic acid was 0.Therefore, the calculated molar ratios of glycolic acid, lactic acid,neopentyl glycol and trimethylol propane were 0.89, 0.1096, 0.00032 and0.00008, respectively. Except for the use of these operation conditions,a polycondensation reaction operation (comprised of the steps (A), (B)and (C)) was performed in substantially the same manner as in item (a)of Example 6, to thereby obtain a glycolic acid copolymer having aweight average molecular weight of 16,000.

During the reaction in step (A), the temperature of the reaction mixturegradually elevated; however, the temperature of the reaction mixturebecame almost constant at 146° C. after the reaction pressure waschanged to 1.0×10⁴ Pa. It was found that the weight average molecularweight of the glycolic acid copolymer just after completion of step (A)was 2,900, and that the weight average molecular weight of the glycolicacid copolymer at the point in time at which the reaction temperaturereached 190° C. was 3,100. It was also found that, from the point intime at which the reaction temperature exceeded 190° C., it took 80minutes for the weight average molecular weight of the glycolic acidcopolymer to reach 10,000. The increasing rate of the weight averagemolecular weight within this period of 80 minutes was 5,175/hour.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 47,300 and a melting temperature of184° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-11”).

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

Subsequently, the above-obtained crystallized glycolic acid copolymerP-11 was subjected to a solid phase polymerization reaction insubstantially the same manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 330,000. The glycolic acid copolymerwas comprised of 88.94% by mole of glycolic acid monomer units; 0.03% bymole of diglycolic acid monomer units; 10.98% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units;0.04% by mole of neopentyl glycol monomer units; and 0.01% by mole oftrimethylol propane monomer units, wherein the lactic acid monomer unitsconstituted a plurality of segments having an average chain length of1.01 in terms of the average number of lactic acid monomer units. Thedegree of discoloration was 33.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the degree ofdiscoloration of the glycolic acid copolymer after the melt heatstability test was 44, which means that the melt heat stability wasfairly good. The oxygen gas permeability of the melt-shaped sheet of theglycolic acid copolymer was 8.6 (cc/m²·day·atm), which means that themelt-shaped sheet had extremely excellent gas barrier property. Further,the strength of the melt-shaped sheet was 5 or more, which means thatthe melt-shaped sheet had the high mechanical strength required ofshaped articles such as a container, a film and the like. Themelt-shaped sheet also had the biodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 3.

EXAMPLE 10

(a) Production of a Glycolic Acid Copolymer

The glycolic acid copolymer having a weight average molecular weight of16,000 (i.e., low molecular weight glycolic acid copolymer) obtained initem (a) of Example 9 was subjected to melt polycondensation reaction insubstantially the same manner as in item (b) of Example 1, to therebyobtain a glycolic acid copolymer.

(c) the Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (a) above was 163,000. The glycolic acid copolymer wascomprised of 88.97% by mole of glycolic acid monomer units; 0.04% bymole of diglycolic acid monomer units; 10.94% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units;0.04% by mole of neopentyl glycol monomer units; and 0.01% by mole oftrimethylol propane monomer units, wherein the lactic acid monomer unitsconstituted a plurality of segments having an average chain length of1.01 in terms of the average number of lactic acid monomer units. Thedegree of discoloration was 39.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(a) above and the properties of a melt-shaped sheet of the glycolic acidcopolymer were evaluated. It was found that the degree of discolorationof the glycolic acid copolymer after the melt heat stability test was48, which means that the melt heat stability was fairly good. The oxygengas permeability of the melt-shaped sheet of the glycolic acid copolymerwas 8.7 (cc/m²·day·atm), which means that the melt-shaped sheet hadextremely excellent gas barrier property. Further, the strength of themelt-shaped sheet was 5 or more, which means that the melt-shaped sheethad the high mechanical strength required of shaped articles such as acontainer, a film and the like. The melt-shaped sheet also had thebiodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 3.

EXAMPLE 11

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 360 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.01% by mole, based onthe molar amount of glycolic acid), 40.83 g of a 90% by weight aqueousL-lactic acid solution, 0.12 g of neopentyl glycol and tetraisopropoxygermanium in an amount of 0.05% by weight, based on the total weight ofthe above-mentioned raw materials (the amount of germanium atom was2.2×10⁻⁶ mole per g of the monomers), to obtain a raw material mixture.The calculated molar ratios of glycolic acid, lactic acid, neopentylglycol and diglycolic acid were 0.89, 0.10957, 0.00034 and 0.00009,respectively. Except for the use of these operation conditions, apolycondensation reaction operation (comprised of the steps (A), (B) and(C)) was performed in substantially the same manner as in item (a) ofExample 6, to thereby obtain a glycolic acid copolymer having a weightaverage molecular weight of 14,300.

During the reaction in step (A), the temperature of the reaction mixturegradually elevated; however, the temperature of the reaction mixturebecame almost constant at 146° C. after the reaction pressure waschanged to 1.0×10⁴ Pa. It was found that the weight average molecularweight of the glycolic acid copolymer just after completion of step (A)was 2,500, and that the weight average molecular weight of the glycolicacid copolymer at the point in time at which the reaction temperaturereached 190° C. was 2,700. It was also found that, from the point intime at which the reaction temperature exceeded 190° C., it took 90minutes for the weight average molecular weight of the glycolic acidcopolymer to reach 10,000. The increasing rate of the weight averagemolecular weight within this period of 90 minutes was 4,867/hour.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by Crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 44,100 and a melting temperature of184° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-12”).

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

Subsequently, the above-obtained crystallized glycolic acid copolymerP-12 was subjected to a solid phase polymerization reaction insubstantially the same manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 186,000. The glycolic acid copolymerwas comprised of 88.96% by mole of glycolic acid monomer units; 0.04% bymole of diglycolic acid monomer units; 10.96% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units; and0.04% by mole of neopentyl glycol monomer units, wherein the lactic acidmonomer units constituted a plurality of segments having an averagechain length of 1.01 in terms of the average number of lactic acidmonomer units. The degree of discoloration was 29.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the degree ofdiscoloration of the glycolic acid copolymer after the melt heatstability test was 40, which means that the melt heat stability wasfairly good. The oxygen gas permeability of the melt-shaped sheet of theglycolic acid copolymer was 8.5 (cc/m²·day·atm), which means that themelt-shaped sheet had extremely excellent gas barrier property. Further,the strength of the melt-shaped sheet was 5 or more, which means thatthe melt-shaped sheet had the high mechanical strength required ofshaped articles such as a container, a film and the like. Themelt-shaped sheet also had the biodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 4.

EXAMPLE 12

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 360 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 40.83 g of a 90% by weightaqueous L-lactic acid solution, 0.12 g of neopentyl glycol, 0.02 g ofoxalic acid and tetraisopropoxy germanium in an amount of 0.05% byweight, based on the total weight of the above-mentioned raw materials(the amount of germanium atom was 2.2×10⁻⁶ mole per g of the monomers),to obtain a raw material mixture. The molar ratio of diglycolic acid inthe obtained raw material mixture was less than 0.00005, so that thecalculated molar ratio of diglycolic acid was 0. Therefore, thecalculated molar ratios of glycolic acid, lactic acid, neopentyl glycoland oxalic acid were 0.89, 0.1096, 0.00034 and 0.00006, respectively.Except for the use of these operation conditions, a polycondensationreaction operation (comprised of the steps (A), (B) and (C)) wasperformed in substantially the same manner as in item (a) of Example 6,to thereby obtain a glycolic acid copolymer having a weight averagemolecular weight of 14,300.

During the reaction in step (A), the temperature of the reaction mixturegradually elevated; however, the temperature of the reaction mixturebecame almost constant at 146° C. after the reaction pressure waschanged to 1.0×10⁴ Pa. It was found that the weight average molecularweight of the glycolic acid copolymer just after completion of step (A)was 2,500, and that the weight average molecular weight of the glycolicacid copolymer at the point in time at which the reaction temperaturereached 190° C. was 2,700. It was also found that, from the point intime at which the reaction temperature exceeded 190° C., it took 90minutes for the weight average molecular weight of the glycolic acidcopolymer to reach 10,000. The increasing rate of the weight averagemolecular weight within this period of 90 minutes was 4,867/hour.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by Crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 44,200 and a melting temperature of184° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-13”).

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

Subsequently, the above-obtained crystallized glycolic acid copolymerP-13 was subjected to a solid phase polymerization reaction insubstantially the same manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 185,000. The glycolic acid copolymerwas comprised of 88.96% by mole of glycolic acid monomer units; 0.03% bymole of diglycolic acid monomer units; 10.96% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units;0.04% by mole of neopentyl glycol monomer units; and 0.01% by mole ofoxalic acid monomer units wherein the lactic acid monomer unitsconstituted a plurality of segments having an average chain length of1.01 in terms of the average number of lactic acid monomer units Thedegree of discoloration was 28.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the degree ofdiscoloration of the glycolic acid copolymer after the melt heatstability test was 39, which means that the melt heat stability wasfairly good. The oxygen gas permeability of the melt-shaped sheet of theglycolic acid copolymer was 8.5 (cc/m²·day·atm), which means that themelt-shaped sheet had extremely excellent gas barrier property. Further,the strength of the melt-shaped sheet was 5 or more, which means thatthe melt-shaped sheet had the high mechanical strength required ofshaped articles such as a container, a film and the like. Themelt-shaped sheet also had the biodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 4.

EXAMPLE 13

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 365 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 36 g of a 90% by weightaqueous L-lactic acid solution, 2.90 g of neopentyl glycol, 3.85 g ofadipic acid and tetraisopropoxy germanium in an amount of 0.05% byweight, based on the total weight of the above-mentioned raw materials(the amount of germanium atom was 2.2×10⁻⁶ mole per g of the monomers),to obtain a raw material mixture. The molar ratio of diglycolic acid inthe obtained raw material mixture was less than 0.00005, so that thecalculated molar ratio of diglycolic acid was 0. Therefore, thecalculated molar ratios of glycolic acid, lactic acid, neopetyl glycoland adipic acid were 0.89, 0.0957, 0.0073 and 0.007, respectively.Except for the use of these operation conditions, a polycondensationreaction operation (comprised of the steps (A), (B) and (C)) wasperformed in substantially the same manner as in item (a) of Example 6,to thereby obtain a glycolic acid copolymer having a weight averagemolecular weight of 14,400.

During the reaction in step (A), the temperature of the reaction mixturegradually elevated; however, the temperature of the reaction mixturebecame almost constant at 146° C. after the reaction pressure waschanged to 1.0×10⁴ Pa. It was found that the weight average molecularweight of the glycolic acid copolymer just after completion of step (A)was 2,500, and that the weight average molecular weight of the glycolicacid copolymer at the point in time at which the reaction temperaturereached 190° C. was 2,700. It was also found that, from the point intime at which the reaction temperature exceeded 190° C., it took 90minutes for the weight average molecular weight of the glycolic acidcopolymer to reach 10,000. The increasing rate of the weight averagemolecular weight within this period of 90 minutes was 4,867/hour.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by Crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 44,500 and a melting temperature of183° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-14”).

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

Subsequently, the above-obtained crystallized glycolic acid copolymerP-14 was subjected to a solid phase polymerization reaction insubstantially the same manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 189,000. The glycolic acid copolymerwas comprised of 88.63% by mole of glycolic acid monomer units; 0.03% bymole of diglycolic acid monomer units; 9.57% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units;0.90% by mole of neopentyl glycol monomer units; and 0.87% by mole ofadipic acid monomer units, wherein the lactic acid monomer unitsconstituted a plurality of segments having an average chain length of1.05 in terms of the average number of lactic acid monomer units. Thedegree of discoloration was 30.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the degree ofdiscoloration of the glycolic acid copolymer after the melt heatstability test was 39, which means that the melt heat stability wasfairly good. The oxygen gas permeability of the melt-shaped sheet of theglycolic acid copolymer was 8.8 (cc/m²·day·atm), which means that themelt-shaped sheet had extremely excellent gas barrier property. Further,the strength of the melt-shaped sheet was 5 or more, which means thatthe melt-shaped sheet had the high mechanical strength required ofshaped articles such as a container, a film and the like. Themelt-shaped sheet also had the biodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 4.

EXAMPLE 14

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 365 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 36 g of a 90% by weightaqueous L-lactic acid solution, 2.80 g of neopentyl glycol, 0.03 g oftrimethylol propane, 3.85 g of adipic acid and tetraisopropoxy germaniumin an amount of 0.05% by weight, based on the total weight of theabove-mentioned raw materials (the amount of germanium atom was 2.2×10⁻⁶mole per g of the monomers), to obtain a raw material mixture. The molarratio of diglycolic acid in the obtained raw material mixture was lessthan 0.00005, so that the calculated molar ratio of diglycolic acid was0. Therefore, the calculated molar ratios of glycolic acid, lactic acid,neopentyl glycol, trimethylol propane and adipic acid were 0.8905,0.09535, 0.00711, 0.00006 and 0.00698, respectively. Except for the useof these operation conditions, a polycondensation reaction operation(comprised of the steps (A), (B) and (C)) was performed in substantiallythe same manner as in item (a) of Example 6, to thereby obtain aglycolic acid copolymer having a weight average molecular weight of15,900.

During the reaction in step (A), the temperature of the reaction mixturegradually elevated; however, the temperature of the reaction mixturebecame almost constant at 146° C. after the reaction pressure waschanged to 1.0×10⁴ Pa. It was found that the weight average molecularweight of the glycolic acid copolymer just after completion of step (A)was 2,800, and that the weight average molecular weight of the glycolicacid copolymer at the point in time at which the reaction temperaturereached 190° C. was 3,000. It was also found that, from the point intime at which the reaction temperature exceeded 190° C., it took 85minutes for the weight average molecular weight of the glycolic acidcopolymer to reach 10,000. The increasing rate of the weight averagemolecular weight within this period of 85 minutes was 4,941/hour.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 46,800 and a melting temperature of180° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-15”).

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

Subsequently, the above-obtained crystallized glycolic acid copolymerP-15 was subjected to a solid phase polymerization reaction insubstantially the same manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 280,000. The glycolic acid copolymerwas comprised of 88.62% by mole of glycolic acid monomer units; 0.03% bymole of diglycolic acid monomer units; 9.56% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units;0.90% by mole of neopentyl glycol monomer units; 0.01% by mole oftrimethylol propane monomer units; and 0.88% by mole of adipic acidmonomer units, wherein the lactic acid monomer units constituted aplurality of segments having an average chain length of 1.01 in terms ofthe average number of lactic acid monomer units. The degree ofdiscoloration was 33.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the degree ofdiscoloration of the glycolic acid copolymer after the melt heatstability test was 42, which means that the melt heat stability wasfairly good. The oxygen gas permeability of the melt-shaped sheet of theglycolic acid copolymer was 9.2 (cc/m²·day·atm), which means that themelt-shaped sheet had extremely excellent gas barrier property. Further,the strength of the melt-shaped sheet was 5 or more, which means thatthe melt-shaped sheet had the high mechanical strength required ofshaped articles such as a container, a film and the like. Themelt-shaped sheet also had the biodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 4.

EXAMPLE 15

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 365 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 30 g of a 90% by weightaqueous L-lactic acid solution, 6.02 g of neopentyl glycol, 8.30 g ofadipic acid and tetraisopropoxy germanium in an amount of 0.05% byweight, based on the total weight of the above-mentioned raw materials(the amount of germanium atom was 2.2×10⁻⁶ mole per g of the monomers),to obtain a raw material mixture. The molar ratio of diglycolic acid inthe obtained raw material mixture was less than 0.00005, so that thecalculated molar ratio of diglycolic acid was 0. Therefore, thecalculated molar ratios of glycolic acid, lactic acid, neopentyl glycoland adipic acid were 0.89, 0.0797, 0.0153 and 0.015, respectively.Except for the use of these operation conditions, a polycondensationreaction operation (comprised of the steps (A), (B) and (C)) wasperformed in substantially the same manner as in item (a) of Example 6,to thereby obtain a glycolic acid copolymer having a weight averagemolecular weight of 14,400.

During the reaction in step (A), the temperature of the reaction mixturegradually elevated; however, the temperature of the reaction mixturebecame almost constant at 146° C. after the reaction pressure waschanged to 1.0×10⁴ Pa. It was found that the weight average molecularweight of the glycolic acid copolymer just after completion of step (A)was 2,500, and that the weight average molecular weight of the glycolicacid copolymer at the point in time at which the reaction temperaturereached 190° C. was 2,700. It was also found that, from the point intime at which the reaction temperature exceeded 190° C., it took 90minutes for the weight average molecular weight of the glycolic acidcopolymer to reach 10,000. The increasing rate of the weight averagemolecular weight within this period of 90 minutes was 4,867/hour.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 44,700 and a melting temperature of182° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-16”).

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

Subsequently, the above-obtained crystallized glycolic acid copolymerP-16 was subjected to a solid phase polymerization reaction insubstantially the same manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 189,000. The glycolic acid copolymerwas comprised of 88.25% by mole of glycolic acid monomer units; 0.03% bymole of diglycolic acid monomer units; 7.93% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units;1.91% by mole of neopentyl glycol monomer units; and 1.88% by mole ofadipic acid monomer units, wherein the lactic acid monomer unitsconstituted a plurality of segments having an average chain length of1.05 in terms of the average number of lactic acid monomer units. Thedegree of discoloration was 30.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the degree ofdiscoloration of the glycolic acid copolymer after the melt heatstability test was 38, which means that the melt heat stability wasfairly good. The oxygen gas permeability of the melt-shaped sheet of theglycolic acid copolymer was 12.0 (cc/m²·day·atm), which means that themelt-shaped sheet had extremely excellent gas barrier property. Further,the strength of the melt-shaped sheet was 5 or more, which means thatthe melt-shaped sheet had the high mechanical strength required ofshaped articles such as a container, a film and the like. Themelt-shaped sheet also had the biodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 4.

COMPARATIVE EXAMPLE 5

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 360 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 15 g of a 90% by weightaqueous L-lactic acid solution, 2.7 g of neopentyl glycol, 3.64 g ofadipic acid and tetraisopropoxy germanium in an amount of 0.05% byweight, based on the total weight of the above-mentioned raw materials(the amount of germanium atom was 2.2×10⁻⁶ mole per g of the monomers),to obtain a raw material mixture. The molar ratio of diglycolic acid inthe obtained raw material mixture was less than 0.00005, so that thecalculated molar ratio of diglycolic acid was 0. Therefore, thecalculated molar ratios of glycolic acid, lactic acid, neopentyl glycoland adipic acid were 0.9428, 0.0427, 0.0074 and 0.0071, respectively.Except for the use of these operation conditions, a polycondensationreaction operation (comprised of the steps (A), (B) and (C)) wasperformed in substantially the same manner as in item (a) of Example 3,to thereby obtain a glycolic acid copolymer having a weight averagemolecular weight of 16,200.

During the reaction in step (A), the temperature of the reaction mixturegradually elevated; however, the temperature of the reaction mixturebecame almost constant at 146° C. after the reaction pressure waschanged to 1.0×10⁴ Pa. It was found that the weight average molecularweight of the glycolic acid copolymer just after completion of step (A)was 1,900, and that the weight average molecular weight of the glycolicacid copolymer at the point in time at which the reaction temperaturereached 190° C. was 2,100. It was also found that, from the point intime at which the reaction temperature exceeded 190° C., it took 80minutes for the weight average molecular weight of the glycolic acidcopolymer to reach 10,000. The increasing rate of the weight averagemolecular weight within this period of 80 minutes was 5,925/hour.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 3, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 44,500 and a melting temperature of208° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-17”).

(B-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

Subsequently, the above-obtained crystallized glycolic acid copolymerP-17 was subjected to a solid phase polymerization reaction insubstantially the same manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 165,000. The glycolic acid copolymerwas comprised of 93.95% by mole of glycolic acid monomer units; 0.03% bymole of diglycolic acid monomer units; 4.21% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units;0.92% by mole of neopentyl glycol monomer units; and 0.89% by mole ofadipic acid monomer units, wherein the lactic acid monomer unitsconstituted a plurality of segments having an average chain length of1.02 in terms of the average number of lactic acid monomer units. Thedegree of discoloration was 34.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the oxygen gaspermeability of the melt-shaped sheet of the glycolic acid copolymer was8.3 (cc/m²·day·atm), which means that the melt-shaped sheet hadextremely excellent gas barrier property. Further, the strength of themelt-shaped sheet was 5 or more, which means that the melt-shaped sheethad the high mechanical strength required of shaped articles such as acontainer, a film and the like. The melt-shaped sheet also had thebiodegradability in soil. However, with respect to the melt heatstability, it was found that the degree of discoloration of the glycolicacid copolymer after the melt heat stability test was 110, and that theglycolic acid copolymer was discolored to assume a brown color.

The results of the analysis and the results of the evaluation are shownin Table 4.

EXAMPLE 16

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 360 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 40.83 g of a 90% by weightaqueous L-lactic acid solution and tetraisopropoxy germanium in anamount of 0.05% by weight, based on the total weight of theabove-mentioned aqueous solutions (the amount of germanium atom was2.2×10⁻⁶ mole per g of the monomers), to obtain a raw material mixture.The separable flask was then purged with nitrogen. The molar ratio ofdiglycolic acid in the obtained raw material mixture was less than0.00005, so that the calculated molar ratio of diglycolic acid was 0.Therefore, the calculated molar ratios of glycolic acid and lactic acidwere 0.89 and 0.11, respectively.

Subsequently, the separable flask was immersed in an oil bath preheatedto 120° C. and, then, stirring of the raw material mixture was performedat a revolution rate of 200 rpm for 1 hour under a stream of nitrogen,thereby effecting a dehydration. Then, a polycondensation reaction wasperformed under conditions wherein the oil bath temperature wasmaintained at 120° C., and the pressure/time conditions weresequentially changed as follows: 8.0×10⁴ Pa for 1 hour, 6.0×10⁴ Pa for 1hour, 5.0×10⁴ Pa for 1 hour, 4.0×10⁴ Pa for 1 hour, 2.5×10⁴ Pa for 1hour, 1.0×10⁴ Pa for 1 hour, 5.0×10³ Pa for 1 hour, and 2.0×10³ Pa for 3hours, to thereby obtain a glycolic acid copolymer. During the reaction,the temperature of the reaction mixture gradually elevated; however, thetemperature of the reaction mixture became almost constant at 116° C.after the reaction pressure was changed to 5.0×10³ Pa. Thus, step (A)was completed. A small portion of the glycolic acid copolymer obtainedin step (A) above was sampled and subjected to measurement of themolecular weight. It was found that the weight average molecular weightof the glycolic acid copolymer was 1,500.

The reaction temperature was gradually elevated to 190° C. over 40minutes while maintaining the revolution rate and the reduced pressure(step (B)). A small portion of the glycolic acid copolymer at the pointin time at which the reaction temperature reached 190° C. was sampledand subjected to measurement of the molecular weight. It was found thatthe weight average molecular weight of the glycolic acid copolymer was1,700.

Subsequently, the reaction temperature was elevated to 200° C. over 10minutes, whereupon the revolution rate was changed to 600 rpm and thereduced pressure was changed to 4.0×10² Pa, followed by performing areaction. The reaction was continued until the total reaction time afterthe reaction temperature exceeded 190° C. became 2.5 hours, therebyobtaining a glycolic acid copolymer having a weight average molecularweight of 13,000 (step (C)). From the point in time at which thereaction temperature exceeded 190° C., it took 110 minutes for theweight average molecular weight of the glycolic acid copolymer to reach10,000. The increasing rate of the weight average molecular weightwithin this period of 110 minutes was 4,527/hour.

The glycolic acid copolymer obtained above in the molten state wascooled to obtain a solidified glycolic acid copolymer having a lowmolecular weight. Then, the obtained low molecular weight glycolic acidcopolymer was taken out of the separable flask and further polymerizedby the operations explained below.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by Crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 42,500 and a melting temperature of184° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-18”).

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

The above-obtained crystallized glycolic acid copolymer P-18 wassubjected to solid phase polymerization reaction in substantially thesame manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 178,000. The glycolic acid copolymerwas comprised of 88.98% by mole of glycolic acid monomer units, 0.02% bymole of diglycolic acid monomer units and 11.00% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units,wherein the lactic acid monomer units constituted a plurality ofsegments having an average chain length of 1.02 in terms of the averagenumber of lactic acid monomer units. The degree of discoloration was 28.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the degree ofdiscoloration of the glycolic acid copolymer after the melt heatstability test was 39, which means that the melt heat stability wasfairly good. The oxygen gas permeability of the melt-shaped sheet of theglycolic acid copolymer was 8.1 (cc/m²·day·atm), which means that themelt-shaped sheet had extremely excellent gas barrier property. Further,the strength of the melt-shaped sheet was 5 or more, which means thatthe melt-shaped sheet had the high mechanical strength required ofshaped articles such as a container, a film and the like. Themelt-shaped sheet also had the biodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 5.

EXAMPLE 17

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

A polycondensation reaction operation (comprised of the steps (A), (B)and (C)) was performed in substantially the same manner as in item (a)of Example 2, except that, in step (A), after the dehydration wasperformed for 1.5 hours under a stream of nitrogen, a polycondensationreaction was performed under conditions wherein the oil bath temperaturewas maintained at 150° C., and the pressure/time conditions weresequentially changed as follows: 5.0×10⁴ Pa for 1 hour, 2.5×10⁴ Pa for0.5 hour, 1.0×10⁴ Pa for 50 minutes and 5.0×10³ Pa for 25 minutes, tothereby obtain a glycolic acid copolymer having a weight averagemolecular weight of 12,800.

During the reaction in step (A), the temperature of the reaction mixturegradually elevated; however, the temperature of the reaction mixturebecame almost constant at 146° C. after the reaction pressure waschanged to 1.0×10⁴ Pa. It was found that the weight average molecularweight of the glycolic acid copolymer just after completion of step (A)was 900, and that the weight average molecular weight of the glycolicacid copolymer at the point in time at which the reaction temperaturereached 190° C. was 1,100. It was also found that, from the point intime at which the reaction temperature exceeded 190° C., it took 110minutes for the weight average molecular weight of the glycolic acidcopolymer to reach 10,000. The increasing rate of the weight averagemolecular weight within this period of 110 minutes was 4,855/hour.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 42,800 and a melting temperature of184° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-1-9”).

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

The above-obtained crystallized glycolic acid copolymer P-19 wassubjected to solid phase polymerization reaction in substantially thesame manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 148,000. The glycolic acid copolymerwas comprised of 88.93% by mole of glycolic acid monomer units, 0.06% bymole of diglycolic acid monomer units and 11.01% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units,wherein the lactic acid monomer units constituted a plurality ofsegments having an average chain length of 1.05 in terms of the averagenumber of lactic acid monomer units. The degree of discoloration was 28.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the degree ofdiscoloration of the glycolic acid copolymer after the melt heatstability test was 44, which means that the melt heat stability wasfairly good. The oxygen gas permeability of the melt-shaped sheet of theglycolic acid copolymer was 8.1 (cc/m²·day·atm), which means that themelt-shaped sheet had extremely excellent gas barrier property. Further,the strength of the melt-shaped sheet was 5 or more, which means thatthe melt-shaped sheet had the high mechanical strength required ofshaped articles such as a container, a film and the like. Themelt-shaped sheet also had the biodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 5.

EXAMPLE 18

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

A polycondensation reaction operation (comprised of the steps (A), (B)and (C)) was performed in substantially the same manner as in Example17, except that, in step (B), the reaction temperature was graduallyelevated to 190° C. over 80 minutes while maintaining the revolutionrate and the reduced pressure, to thereby obtain a glycolic acidcopolymer having a weight average molecular weight of 13,800.

During the reaction in step (A), the temperature of the reaction mixturegradually elevated; however, the temperature of the reaction mixturebecame almost constant at 146° C. after the reaction pressure waschanged to 1.0×10⁴ Pa. It was found that the weight average molecularweight of the glycolic acid copolymer just after completion of step (A)was 900, and that the weight average molecular weight of the glycolicacid copolymer at the point in time at which the reaction temperaturereached 190° C. was 2,100. It was also found that, from the point intime at which the reaction temperature exceeded 190° C., it took 100minutes for the weight average molecular weight of the glycolic acidcopolymer to reach 10,000. The increasing rate of the weight averagemolecular weight within this period of 100 minutes was 4,740/hour.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by Crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 43,500 and a melting temperature of185° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-20”).

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

The above-obtained crystallized glycolic acid copolymer P-20 wassubjected to solid phase polymerization reaction in substantially thesame manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 132,000. The glycolic acid copolymerwas comprised of 88.91% by mole of glycolic acid monomer units, 0.08% bymole of diglycolic acid monomer units and 11.01% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units,wherein the lactic acid monomer units constituted a plurality ofsegments having an average chain length of 1.02 in terms of the averagenumber of lactic acid monomer units. The degree of discoloration was 28.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the degree ofdiscoloration of the glycolic acid copolymer after the melt heatstability test was 48, which means that the melt heat stability wasfairly good. The oxygen gas permeability of the melt-shaped sheet of theglycolic acid copolymer was 8.0 (cc/m²·day·atm), which means that themelt-shaped sheet had extremely excellent gas barrier property. Further,the strength of the melt-shaped sheet was 5 or more, which means thatthe melt-shaped sheet had the high mechanical strength required ofshaped articles such as a container, a film and the like. Themelt-shaped sheet also had the biodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 5.

EXAMPLE 19

(a) Production of a low molecular weight glycolic acid Copolymer

A polycondensation reaction operation (comprised of the steps (A), (B)and (C)) was performed in substantially the same manner as in item (a)of Example 2, except that, after completion of step (B), the reactiontemperature was gradually elevated to 200° C. over 10 minutes whilemaintaining the revolution rate at 200 rpm, and that in step (C), thereaction was continued until the total reaction time after the reactiontemperature exceeded 190° C. became 6 hours, to thereby obtain aglycolic acid copolymer having a weight average molecular weight of12,000.

During the reaction in step (A), the temperature of the reaction mixturegradually elevated; however, the temperature of the reaction mixturebecame almost constant at 146° C. after the reaction pressure waschanged to 1.0×10⁴ Pa. It was found that the weight average molecularweight of the glycolic acid copolymer just after completion of step (A)was 1,900, and that the weight average molecular weight of the glycolicacid copolymer at the point in time at which the reaction temperaturereached 190° C. was 2,100. It was also found that, from the point intime at which the reaction temperature exceeded 190° C., it took 290minutes for the weight average molecular weight of the glycolic acidcopolymer to reach 10,000. The increasing rate of the weight averagemolecular weight within this period of 290 minutes was 1,634/hour.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 42,800 and a melting temperature of184° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-21”).

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

The above-obtained crystallized glycolic acid copolymer P-21 wassubjected to solid phase polymerization reaction in substantially thesame manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 152,000. The glycolic acid copolymerwas comprised of 88.92% by mole of glycolic acid monomer units, 0.07% bymole of diglycolic acid monomer units and 11.01% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units,wherein the lactic acid monomer units constituted a plurality ofsegments having an average chain length of 1.02 in terms of the averagenumber of lactic acid monomer units. The degree of discoloration was 28.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the degree ofdiscoloration of the glycolic acid copolymer after the melt heatstability test was 46, which means that the melt heat stability wasfairly good. The oxygen gas permeability of the melt-shaped sheet of theglycolic acid copolymer was 8.0 (cc/m²·day·atm), which means that themelt-shaped sheet had extremely excellent gas barrier property. Further,the strength of the melt-shaped sheet was 5 or more, which means thatthe melt-shaped sheet had the high mechanical strength required ofshaped articles such as a container, a film and the like. Themelt-shaped sheet also had the biodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 5.

EXAMPLE 20

The glycolic acid copolymer produced in item “(a) Production of a lowmolecular weight glycolic acid copolymer” of Example 16 was subjected tomelt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, except thatthe reaction time was changed to 1.5 hours, to thereby obtain apulverized, crystallized glycolic acid copolymer having a weight averagemolecular weight of 20,000 and a melting temperature of 185° C.(hereinafter referred to as “crystallized glycolic acid copolymerP-22”).

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained Above

The above-obtained crystallized glycolic acid copolymer P-22 wassubjected to solid phase polymerization reaction in substantially thesame manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 93,000. The glycolic acid copolymer wascomprised of 88.98% by mole of glycolic acid monomer units, 0.02% bymole of diglycolic acid monomer units and 11.00% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units,wherein the lactic acid monomer units constituted a plurality ofsegments having an average chain length of 1.02 in terms of the averagenumber of lactic acid monomer units. The degree of discoloration was 27.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the degree ofdiscoloration of the glycolic acid copolymer after the melt heatstability test was 38, which means that the melt heat stability wasfairly good. The oxygen gas permeability of the melt-shaped sheet of theglycolic acid copolymer was 8.1 (cc/m²·day·atm), which means that themelt-shaped sheet had extremely excellent gas barrier property. Further,the strength of the melt-shaped sheet was 4, which means that themelt-shaped sheet had the high mechanical strength required of shapedarticles such as a container, a film and the like. The melt-shaped sheetalso had the biodegradability in soil.

The results of the analysis and the results of the evaluation are shownin Table 5.

COMPARATIVE EXAMPLE 6

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 349 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 39.3 g of a 90% by weightaqueous L-lactic acid solution, 0.60 g of neopentyl glycol andtetraisopropoxy germanium in an amount of 0.05% by weight, based on thetotal weight of the above-mentioned raw materials (the amount ofgermanium atom was 2.2×10⁻⁶ mole per g of the monomers), to obtain a rawmaterial mixture. The separable flask was then purged with nitrogen.

The molar ratio of diglycolic acid in the obtained raw material mixturewas less than 0.00005, so that the calculated molar ratio of diglycolicacid was 0. Therefore, the calculated molar ratios of glycolic acid,lactic acid and neopentyl glycol were 0.8896, 0.1088 and 0.0016,respectively.

Subsequently, the separable flask was immersed in an oil bath preheatedto 150° C. and, then, stirring of the raw material mixture was performedat a revolution rate of 100 rpm for 1.5 hours under a stream ofnitrogen, thereby effecting a dehydration. Then, a polycondensationreaction was performed under conditions wherein the oil bath temperaturewas maintained at 150° C., and the pressure/time conditions weresequentially changed as follows: 5.0×10⁴ Pa for 1 hour, 2.5×10⁴ Pa for0.5 hour and 1.0×10⁴ Pa for 20 minutes, to thereby obtain a glycolicacid copolymer. During the reaction, the temperature of the reactionmixture gradually elevated; however, the temperature of the reactionmixture became almost constant at 146° C. after the reaction pressurewas changed to 1.0×10⁴ Pa. A small portion of the glycolic acidcopolymer just after the above reaction was sampled and subjected tomeasurement of the molecular weight. It was found that the weightaverage molecular weight of the glycolic acid copolymer was 400.

The reaction temperature was gradually elevated to 190° C. over 120minutes while maintaining the revolution rate and the reduced pressure.A small portion of the glycolic acid copolymer at the point in time atwhich the reaction temperature reached 190° C. was sampled and subjectedto measurement of the molecular weight. It was found that the weightaverage molecular weight of the glycolic acid copolymer was 700.Subsequently, the reaction temperature was elevated to 200° C. over 10minutes, whereupon the revolution rate was changed to 600 rpm and thereduced pressure was changed to 4.0×10² Pa, followed by performing areaction. The reaction was continued until the total reaction time afterthe reaction temperature exceeded 190° C. became 3 hours, therebyobtaining a glycolic acid copolymer having a weight average molecularweight of 14,600. From the point in time at which the reactiontemperature exceeded 190° C., it took 120 minutes for the weight averagemolecular weight of the glycolic acid copolymer to reach 10,000. Theincreasing rate of the weight average molecular weight within thisperiod of 120 minutes was 4,650/hour.

The glycolic acid copolymer obtained above in the molten state wascooled to obtain a solidified glycolic acid copolymer having a lowmolecular weight. Then, the obtained low molecular weight glycolic acidcopolymer was taken out of the separable flask and further polymerizedby the operations explained below.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by Crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 42,000 and a melting temperature of183° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-23”).

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

The above-obtained crystallized glycolic acid copolymer P-23 wassubjected to solid phase polymerization reaction in substantially thesame manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 186,000. The glycolic acid copolymerwas comprised of 88.59% by mole of glycolic acid monomer units, 0.20% bymole of diglycolic acid monomer units and 11.00% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units and0.21% by mole of neopentyl glycol monomer units, wherein the lactic acidmonomer units constituted a plurality of segments having an averagechain length of 1.02 in terms of the average number of lactic acidmonomer units. The degree of discoloration was 40.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the oxygen gaspermeability of the melt-shaped sheet of the glycolic acid copolymer was8.7 (cc/m²·day·atm), which means that the melt-shaped sheet hadextremely excellent gas barrier property. Further, the strength of themelt-shaped sheet was 5 or more, which means that the melt-shaped sheethad the high mechanical strength required of shaped articles such as acontainer, a film and the like. The melt-shaped sheet also had thebiodegradability in soil. However, with respect to the melt heatstability, it was found that the degree of discoloration of the glycolicacid copolymer after the melt heat stability test was 224, and that theglycolic acid copolymer was discolored to assume a brown color.

The results of the analysis and the results of the evaluation are shownin Table 6.

COMPARATIVE EXAMPLE 7

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 349 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 39.3 g of a 90% by weightaqueous L-lactic acid solution, 0.60 g of neopentyl glycol andtetraisopropoxy germanium in an amount of 0.05% by weight, based on thetotal weight of the above-mentioned aqueous solutions (the amount ofgermanium atom was 2.2×10⁻⁶ mole per g of the monomers), to obtain a rawmaterial mixture. The separable flask was then purged with nitrogen.

The molar ratio of diglycolic acid in the obtained raw material mixturewas less than 0.00005, so that the calculated molar ratio of diglycolicacid was 0. Therefore, the calculated molar ratios of glycolic acid,lactic acid and neopentyl glycol were 0.8896, 0.1088 and 0.0016,respectively.

Subsequently, the separable flask was immersed in an oil bath preheatedto 150° C. and, then, stirring of the raw material mixture was performedat a revolution rate of 100 rpm for 1.5 hours under a stream ofnitrogen, thereby effecting a dehydration. Then, a polycondensationreaction was performed under conditions wherein the oil bath temperaturewas maintained at 150° C., and the pressure/time conditions weresequentially changed as follows: 5.0×10⁴ Pa for 1 hour, 2.5×10⁴ Pa for0.5 hour and 1.0×10⁴ Pa for 20 minutes, to thereby obtain a glycolicacid copolymer.

During the reaction, the temperature of the reaction mixture graduallyelevated; however, the temperature of the reaction mixture became almostconstant at 146° C. after the reaction pressure was changed to 1.0×10⁴Pa. A small portion of the glycolic acid copolymer obtained in the abovereaction was sampled and subjected to measurement of the molecularweight. It was found that the weight average molecular weight of theglycolic acid copolymer was 400.

The reaction temperature was gradually elevated to 190° C. over 25minutes while maintaining the revolution rate and the reduced pressure.A small portion of the glycolic acid copolymer at the point in time atwhich the reaction temperature reached 190° C. was sampled and subjectedto measurement of the molecular weight. It was found that the weightaverage molecular weight of the glycolic acid copolymer was 500.Subsequently, the reaction temperature was elevated to 200° C. over 10minutes, whereupon the reduced pressure was changed to 6.0×10² Pa,followed by performing a reaction while maintaining the revolution rateat 100 rpm. The reaction was continued until the total reaction timeafter the reaction temperature exceeded 190° C. became 20 hours, therebyobtaining a glycolic acid copolymer having a weight average molecularweight of 14,500. From the point in time at which the reactiontemperature exceeded 190° C., it took 810 minutes for the weight averagemolecular weight of the glycolic acid copolymer to reach 10,000. Theincreasing rate of the weight average molecular weight within thisperiod of 810 minutes was 704/hour.

The glycolic acid copolymer obtained above in the molten state wascooled to obtain a solidified glycolic acid copolymer having a lowmolecular weight. Then, the obtained low molecular weight glycolic acidcopolymer was taken out of the separable flask and further polymerizedby the operations explained below.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by Crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 44,000 and a melting temperature of182° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-24”).

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

The above-obtained crystallized glycolic acid copolymer P-24 wassubjected to solid phase polymerization reaction in substantially thesame manner as in item (b-2) of Example 2.

(c) The results of the analysis of the glycolic acid copolymer Theweight average molecular weight of the glycolic acid copolymer obtainedin item (b-2) above was 179,000. The glycolic acid copolymer wascomprised of 88.58% by mole of glycolic acid monomer units, 0.21% bymole of diglycolic acid monomer units, 11.00% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units and0.21% by mole of neopentyl glycol monomer units, wherein the lactic acidmonomer units constituted a plurality of segments having an averagechain length of 1.02 in terms of the average number of lactic acidmonomer units. The degree of discoloration was 39.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the oxygen gaspermeability of the melt-shaped sheet of the glycolic acid copolymer was8.8 (cc/m²·day·atm), which means that the melt-shaped sheet hadextremely excellent gas barrier property. Further, the strength of themelt-shaped sheet was 5 or more, which means that the melt-shaped sheethad the high mechanical strength required of shaped articles such as acontainer, a film and the like. The melt-shaped sheet also had thebiodegradability in soil. However, with respect to the melt heatstability, it was found that the degree of discoloration of the glycolicacid copolymer after the melt heat stability test was 242, and that theglycolic acid copolymer was discolored to assume a brown color.

The results of the analysis and the results of the evaluation are shownin Table 6.

COMPARATIVE EXAMPLE 8

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 349 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 39.3 g of a 90% by weightaqueous L-lactic acid solution, 0.60 g of neopentyl glycol andtetraisopropoxy germanium in an amount of 0.05% by weight, based on thetotal weight of the above-mentioned raw materials (the amount ofgermanium atom was 2.2×10⁻⁶ mole per g of the monomers), to obtain a rawmaterial mixture. The separable flask was then purged with nitrogen.

The molar ratio of diglycolic acid in the obtained raw material mixturewas less than 0.00005, so that the calculated molar ratio of diglycolicacid was 0. Therefore, the calculated molar ratios of glycolic acid,lactic acid and neopentyl glycol were 0.8896, 0.1088 and 0.0016,respectively.

Subsequently, the separable flask was immersed in an oil bath preheatedto 150° C. and, then, stirring of the raw material mixture was performedat a revolution rate of 100 rpm for 1.5 hours under a stream ofnitrogen, thereby effecting a dehydration. Then, a polycondensationreaction was performed under conditions wherein the oil bath temperaturewas maintained at 150° C., and the pressure/time conditions weresequentially changed as follows: 5.0×10⁴ Pa for 1 hour, 2.5×10⁴ Pa for0.5 hour, 1.0×10⁴ Pa for 50 minutes and 5.0×10³ Pa for 20 minutes, tothereby obtain a glycolic acid copolymer.

During the reaction, the temperature of the reaction mixture graduallyelevated; however, the temperature of the reaction mixture became almostconstant at 146° C. after the reaction pressure was changed to 1.0×10⁴Pa.

A small portion of the glycolic acid copolymer obtained in the abovereaction was sampled and subjected to measurement of the molecularweight. It was found that the weight average molecular weight of theglycolic acid copolymer was 900.

The reaction temperature was gradually elevated to 190° C. over 120minutes while maintaining the revolution rate and the reduced pressure.A small portion of the glycolic acid copolymer at the point in time atwhich the reaction temperature reached 190° C. was sampled and subjectedto measurement of the molecular weight. It was found that the weightaverage molecular weight of the glycolic acid copolymer was 1,500.Subsequently, the reaction temperature was elevated to 200° C. over 10minutes, whereupon the reduced pressure was changed to 6.0×10² Pa,followed by performing a reaction while maintaining the revolution rateat 100 rpm. The reaction was continued until the total reaction timeafter the reaction temperature exceeded 190° C. became 20 hours, therebyobtaining a glycolic acid copolymer having a weight average molecularweight of 15,600. From the point in time at which the reactiontemperature exceeded 190° C., it took 720 minutes for the weight averagemolecular weight of the glycolic acid copolymer to reach 10,000. Theincreasing rate of the weight average molecular weight within thisperiod of 720 minutes was 708/hour.

The glycolic acid copolymer obtained above in the molten state wascooled to obtain a solidified glycolic acid copolymer having a lowmolecular weight. Then, the obtained low molecular weight glycolic acidcopolymer was taken out of the separable flask and further polymerizedby the operations explained below.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 44,800 and a melting temperature of182° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-25”).

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

The above-obtained crystallized glycolic acid copolymer P-25 wassubjected to solid phase polymerization reaction in substantially thesame manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 184,000. The glycolic acid copolymerwas comprised of 88.62% by mole of glycolic acid monomer units, 0.18% bymole of diglycolic acid monomer units, 11.00% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units and0.20% by mole of neopentyl glycol monomer units, wherein the lactic acidmonomer units constituted a plurality of segments having an averagechain length of 1.02 in terms of the average number of lactic acidmonomer units. The degree of discoloration was 37.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the oxygen gaspermeability of the melt-shaped sheet of the glycolic acid copolymer was8.8 (cc/m²·day·atm), which means that the melt-shaped sheet hadextremely excellent gas barrier property. Further, the strength of themelt-shaped sheet was 5 or more, which means that the melt-shaped, sheethad the high mechanical strength required of shaped articles such as acontainer, a film and the like. The melt-shaped sheet also had thebiodegradability in soil. However, with respect to the melt heatstability, it was found that the degree of discoloration of the glycolicacid copolymer after the melt heat stability test was 196, and that theglycolic acid copolymer was discolored to assume a brown color.

The results of the analysis and the results of the evaluation are shownin Table 6.

COMPARATIVE EXAMPLE 9

(a) Production of a Low Molecular Weight Glycolic Acid Copolymer

Into substantially the same reaction apparatus (separable flask) as inExample 1 were introduced 360 g of a 70% by weight aqueous glycolic acidsolution (having a diglycolic acid content of 0.005% by mole or less,based on the molar amount of glycolic acid), 40.83 g of a 90% by weightaqueous L-lactic acid solution and tetraisopropoxy germanium in anamount of 0.05% by weight, based on the total weight of theabove-mentioned aqueous solutions (the amount of germanium atom was2.2×10⁻⁶ mole per g of the monomers), to obtain a raw material mixture.The separable flask was then purged with nitrogen.

The molar ratio of diglycolic acid in the obtained raw material mixturewas less than 0.00005, so that the calculated molar ratio of diglycolicacid was 0. Therefore, the calculated molar ratios of glycolic acid andlactic acid were 0.89 and 0.11, respectively.

Subsequently, the separable flask was immersed in an oil bath preheatedto 180° C. and, then, stirring of the raw material mixture was performedat a revolution rate of 200 rpm for 3 hours under a stream of nitrogen,thereby effecting a dehydration. Then, a polycondensation reaction wasperformed under conditions wherein the oil bath temperature wasmaintained at 180° C., and the pressure/time conditions weresequentially changed as follows: 5.0×10⁴ Pa for 1 hour, 2.5×10⁴ Pa for0.5 hour, 1.0×10⁴ Pa for 30 minutes, 5.0×10³ Pa for 30 minutes and2.0×10³ Pa for 20 minutes, to thereby obtain a glycolic acid copolymer.

In the above reaction (which was performed in the separable flaskimmersed in the oil bath preheated to 180° C.), it was found that theweight average molecular weight of the glycolic acid copolymer asmeasured at the point in time at which the reaction temperature exceeded160° C. was 300. A small portion of the glycolic acid copolymer obtainedafter completion of the above reaction was sampled and subjected tomeasurement of the molecular weight. It was found that the weightaverage molecular weight of the glycolic acid copolymer was 2,200.

The reaction temperature was gradually elevated to 190° C. over 15minutes while maintaining the revolution rate and the reduced pressure.A small portion of the glycolic acid copolymer at the point in time atwhich the reaction temperature reached 190° C. was sampled and subjectedto measurement of the molecular weight. It was found that the weightaverage molecular weight of the glycolic acid copolymer was 2,300.

Subsequently, the reaction temperature was elevated to 200° C. over 10minutes, whereupon the revolution rate was changed to 600 rpm and thereduced pressure was changed to 4.0×10² Pa, followed by performing areaction. The reaction was continued until the total reaction time afterthe reaction temperature exceeded 190° C. became 2.5 hours, therebyobtaining a glycolic acid copolymer having a weight average molecularweight of 14,100.

The glycolic acid copolymer obtained above in the molten state wascooled to obtain a solidified glycolic acid copolymer having a lowmolecular weight. Then, the obtained low molecular weight glycolic acidcopolymer was taken out of the separable flask and further polymerizedby the operations explained below.

(b) Melt Polycondensation of a Low Molecular Weight Glycolic AcidCopolymer, Followed by Crystallization, Pulverization and Solid PhasePolymerization

(b-1) Melt Polycondensation, Crystallization and Pulverization

The low molecular weight glycolic acid copolymer obtained above wassubjected to melt polycondensation, crystallization and pulverization insubstantially the same manner as in item (b-1) of Example 2, to therebyobtain a pulverized, crystallized glycolic acid copolymer having aweight average molecular weight of 43,600 and a melting temperature of183° C. (hereinafter referred to as “crystallized glycolic acidcopolymer P-26”).

(b-2) Solid Phase Polymerization of the Pulverized, CrystallizedGlycolic Acid Copolymer Obtained in Item (b-1)

The above-obtained crystallized glycolic acid copolymer P-26 wassubjected to solid phase polymerization reaction in substantially thesame manner as in item (b-2) of Example 2.

(c) The Results of the Analysis of the Glycolic Acid Copolymer

The weight average molecular weight of the glycolic acid copolymerobtained in item (b-2) above was 109,000. The glycolic acid copolymerwas comprised of 88.84% by mole of glycolic acid monomer units, 0.14% bymole of diglycolic acid monomer units and 11.02% by mole of lactic acidmonomer units as non-glycolic, hydroxycarboxylic acid monomer units,wherein the lactic acid monomer units constituted a plurality ofsegments having an average chain length of 1.02 in terms of the averagenumber of lactic acid monomer units. The degree of discoloration was 38.

(d) Evaluation of the Glycolic Acid Copolymer and a Melt-Shaped Sheet ofthe Glycolic Acid Copolymer

The melt heat stability of the glycolic acid copolymer obtained in item(b-2) above and the properties of a melt-shaped sheet of the glycolicacid copolymer were evaluated. It was found that the oxygen gaspermeability of the melt-shaped sheet of the glycolic acid copolymer was8.3 (cc/m²·day·atm), which means that the melt-shaped sheet hadextremely excellent gas barrier property. Further, the strength of themelt-shaped sheet was 4, which means that the melt-shaped sheet had thehigh mechanical strength required of shaped articles such as acontainer, a film and the like. The melt-shaped sheet also had thebiodegradability in soil. However, with respect to the melt heatstability, it was found that the degree of discoloration of the glycolicacid copolymer after the melt heat stability test was 158, and that theglycolic acid copolymer was discolored to assume a brown color.

The results of the analysis and the results of the evaluation are shownin Table 6.

REFERENCE EXAMPLE 1

A glycolic acid-lactic acid copolymer was produced by a ring-openingpolymerization as follows.

(a) Preparation of the Raw Materials (Monomers)

(a-1) Preparation of a Purified Glycolide

250 g of glycolide was dissolved in 500 g of dehydrated ethyl acetate at75° C. The resultant solution was allowed to stand still at roomtemperature for 10 hours, thereby precipitating the glycolide, followedby filtration, thereby recovering the resultant precipitate. Theobtained precipitate was washed with about 500 g of dehydrated ethylacetate at room temperature. The washing of the precipitate was thenrepeated once. The washed precipitate was placed in an eggplant shapedflask, and the flask was immersed in an oil bath preheated at 60° C.,followed by vacuum drying for 24 hours, to thereby obtain a driedproduct. The obtained dried product was subjected to simpledistillation, to thereby obtain 95 g of a purified glycolide (having aboiling point of from 133 to 134° C. under a reduced pressure of from9×10² to 8×10² Pa). The obtained purified glycolide was preserved underdry nitrogen before subjected to the polymerization reaction describedbelow.

(a-2) Preparation of a Purified Lactide

250 g of L-lactide was dissolved in 500 g of dehydrated toluene at 80°C. The resultant solution was allowed to stand still at room temperaturefor 10 hours, thereby precipitating the L-lactide, followed byfiltration, thereby recovering the resultant precipitate. The obtainedprecipitate was washed with about 500 g of dehydrated toluene at roomtemperature. The washing of the precipitate was then repeated once. Thewashed precipitate was placed in an eggplant shaped flask, and the flaskwas immersed in an oil bath preheated at 60° C., followed by vacuumdrying for 24 hours, to thereby obtain 120 g of a purified L-lactide.The obtained purified L-lactide was preserved under dry nitrogen beforesubjected to the following polymerization reaction.

(b-1) Production of Glycolic Acid Copolymer (i)

Into a well dried, pressure-resistant tube (having a Teflon-coatedinside surface) under dry nitrogen were introduced 84 g of the purifiedglycolide obtained in item (a-1) above, 19 g of the purified lactideobtained in item (a-2) above, 0.03 g of stannous 2-ethyl-hexanoate as acatalyst and 0.01 g of dehydrated lauryl alcohol. The tube was cappedand then immersed in a shaking oil bath preheated at 130° C., followedby shaking of the tube for 20 hours to thereby effect a polymerizationreaction. After completion of the polymerization, the tube was cooled toroom temperature, and the contents of the tube (i.e., a reactionproduct) were taken out. The obtained reaction product, which was a bulkpolymer, was then subjected to pulverization to thereby obtain particleshaving a particle diameter of about 1 mm or less. The obtained particleswere extracted with dehydrated ethyl acetate using a Soxhlet extractorfor 10 hours. The resultant extract was then subjected to vacuum dryingfor 24 hours using a vacuum dryer, to thereby obtain 95 g of glycolicacid copolymer (i).

(b-2) Production of Glycolic Acid Copolymer (ii)

Into a well dried, pressure resistant tube (having a Teflon-coatedinside surface) under dry nitrogen were introduced 84 g of the purifiedglycolide obtained in item (a-1) above, 39 g of the purified lactideobtained in item (a-2) above, 0.037 g of stannous 2-ethyl-hexanoate as acatalyst and 0.012 g of dehydrated lauryl alcohol. The tube was cappedand then immersed in a shaking oil bath preheated at 130° C., followedby shaking of the tube for 20 hours to thereby effect a polymerizationreaction. After completion of the polymerization, the tube was cooled toroom temperature, and the contents of the tube (i.e., a reactionproduct) were taken out. The reaction product, which was a bulk polymer,was then subjected to pulverization to thereby obtain particles having aparticle diameter of about 1 mm or less. The obtained particles wereextracted with dehydrated ethyl acetate using a Soxhlet extractor for 10hours. The resultant extract was then subjected to vacuum drying for 24hours using a vacuum dryer, to thereby obtain 116 g of glycolic acidcopolymer (ii).

COMPARATIVE EXAMPLE 10

(a) The Results of the Analysis of Glycolic Acid Copolymer (i) Producedby a Ring-Opening Polymerization

The weight average molecular weight of glycolic acid copolymer (i)obtained by a ring-opening polymerization in item (b-1) in ReferenceExample 1 was 175,000. Glycolic acid copolymer (i) was comprised of94.00% by mole of glycolic acid monomer units and 6.00% by mole oflactic acid monomer units as non-glycolic, hydroxycarboxylic acidmonomer units, wherein the lactic acid monomer units constituted aplurality of segments having an average chain length of 2.08 in terms ofthe average number of lactic acid monomer units. Diglycolic acid monomerunits were not observed. The degree of discoloration was 30.

(b) Evaluation of Glycolic Acid Copolymer (I) and a Melt-Shaped Sheet ofGlycolic Acid Copolymer (i)

The melt heat stability of the glycolic acid copolymer (i) obtained initem (b-1) of Reference Example 1 and the properties of a melt-shapedsheet of glycolic acid copolymer (i) were evaluated. It was found thatthe oxygen gas permeability of the melt-shaped sheet of glycolic acidcopolymer (i) was 8.8 (cc/m²·day·atm), which means that the melt-shapedsheet had extremely excellent gas barrier property. Further, thestrength of the melt-shaped sheet was 5 or more, which means that themelt-shaped sheet had the high mechanical strength required of shapedarticles such as a container, a film and the like. The melt-shaped sheetalso had the biodegradability in soil. However, with respect to the meltheat stability, it was found that the degree of discoloration ofglycolic acid copolymer (i) after the melt heat stability test was 92,and that glycolic acid copolymer (i) was discolored to assume a yellowcolor.

The results of the analysis and the results of the evaluation are shownin Table 6.

COMPARATIVE EXAMPLE 11

(a) The Results of the Analysis of Glycolic Acid Copolymer (ii) Producedby a Ring-Opening Polymerization

The weight average molecular weight of glycolic acid copolymer (ii)obtained by a ring-opening polymerization in item (b-2) in ReferenceExample 1 was 183,000. Glycolic acid copolymer (ii) was comprised of83.00% by mole of glycolic acid monomer units and 17.00% by mole oflactic acid monomer units as non-glycolic, hydroxycarboxylic acidmonomer units, wherein the lactic acid monomer units constituted aplurality of segments having an average chain length of 2.36 in terms ofthe average number of lactic acid monomer units. Diglycolic acid monomerunits were not observed. The degree of discoloration was 29.

(b) Evaluation of Glycolic Acid Copolymer (Ii) and a Melt-Shaped Sheetof Glycolic Acid Copolymer (ii)

The melt heat stability of the glycolic acid copolymer (ii) obtained initem (b-2) of Reference Example 1 and the properties of a melt-shapedsheet of glycolic acid copolymer (ii) were evaluated. It was found thatthe strength of the melt-shaped sheet was 5 or more, which means thatthe melt-shaped sheet had the high mechanical strength required ofshaped articles such as a container, a film and the like. Themelt-shaped sheet also had the biodegradability in soil. However, theoxygen gas permeability of the melt-shaped sheet of the glycolic acidcopolymer was 28 (cc/m² day·atm), which means that the gas barrierproperty of the melt-shaped sheet was poor. Further, with respect to themelt heat stability, it was found that the degree of discoloration ofglycolic acid copolymer (ii) after the melt heat stability test was 58,and that glycolic acid copolymer (ii) was discolored to assume a yellowcolor.

The results of the analysis and the results of the evaluation are shownin Table 6.

REFERENCE EXAMPLE 2

The glycolic acid copolymer obtained in item (b-2) of Example 11 wassubjected to measurement of the weight average molecular weight insubstantially the same manner as in Example 11, except thathexafluoroisopropanol containing no sodium trifluoroacetate dissolvedtherein was used as an eluent. It was found that the glycolic acidcopolymer had a weight average molecular weight of 583,000. TABLE 1Example 1 Example 2 Example 3 Example 4 Example 5 Results of Weightaverage molecular weight 123,000 186,000 182,000 167,000 179,000 the(Mw) analysis Content of glycolic acid monomer 83.97 88.97 93.97 88.9788.97 of the units (% by mole) obtained Non-glycolic, Type Lactic acidLactic acid Lactic acid 6-hydroxyhexanoic 3-hydroxybutylic copolymerhydroxycarboxylic acid acid acid Content (% by 16.00 11.00 6.00 11.0011.00 monomer units mole) Average chain 1.08 1.02 1.02 1.03 1.02 lengthContent of diglycolic acid monomer 0.03 0.03 0.03 0.03 0.03 units (% byweight) Polyol monomer Type — — — — — units Content (% by — — — — —mole) Polycarboxylic Type — — — — — acid monomer Content (% by — — — — —units mole) Total content of polycarboxylic acid 0.03 0.03 0.03 0.030.03 monomer units including polyol monomer units and diglycolic acidmonomer units (% by mole) Degree of discoloration of copolymer 28 29 2929 28 Results of Degree of discoloration after the 36 38 43 38 39evaluation melt heat stability test Oxygen gas permeability of the 9.18.0 7.2 8.1 8.0 melt-shaped sheet (cc/m² · day · atm) Strength of themelt-shaped sheet 4 5 or more 5 or more 5 or more 5 or moreBiodegradability of the melt-shaped Bio- Biodegradable BiodegradableBiodegradable Biodegradable sheet in soil degradableNote:“—” means “not detected”.

TABLE 2 Comparative Comparative Comparative Comparative Example 1Example 2 Example 3 Example 4 Results of Weight average molecular weight(Mw) 109,000 164,000 122,000 187,000 the Content of glycolic acidmonomer unit (% by 88.86 96.97 72.96 88.97 analysis weight) of theNon-glycolic, Type Lactic acid Lactic acid Lactic acid Lactic acidobtained hydroxycarboxylic acid Content (% by mole) 11.01 3.00 27.0111.00 copolymer monomer units Average chain length 1.02 1.01 1.14 1.62Content of diglycolic acid monomer unit (% by 0.13 0.03 0.03 0.03 mole)Polyol monomer units Type — — — — Content (% by mole) — — — —Polycarboxylic acid Type — — — — monomer units Content (% by mole) — — —— Total content of polycarboxylic acid monomer 0.13 0.03 0.03 0.03 unitsincluding polyol monomer units and diglycolic acid monomer units (% bymole) Degree of discoloration of copolymer 34 33 33 29 Results of Degreeof discoloration after the melt heat 175 115 39 105 evaluation stabilitytest Oxygen gas permeability of a melt-shaped sheet 8.2 7.0 35.0 8.4(cc/m² · day · atm) Strength of the melt-shaped sheet 4 5 or more 4 5 ormore Biodegradability of the melt-shaped sheet in soil BiodegradableBiodegradable Biodegradable BiodegradableNote:“—” means “not detected”.

TABLE 3 Example 6 Example 7 Example 8 Example 9 Example 10 ResultsWeight average molecular weight (Mw) 187,000 187,000 325,000 330,000163,000 of Content of glycolic acid monomer units 88.94 88.94 88.9888.94 88.97 the (% by mole) analysis Non-glycolic, Type Lactic acidLactic acid Lactic acid Lactic acid Lactic acid of the hydroxycarboxylicContent 10.99 10.99 10.98 10.98 10.94 obtained acid monomer units (% bymole) copolymer Average chain 1.01 1.01 1.01 1.01 1.01 length Content ofdiglycolic acid monomer unit 0.03 0.03 0.03 0.03 0.04 (% by mole) Polyolmonomer Type Neopentyl 1,6- Trimethylol- Neopentyl Trimethylol-Neopentyl Trimethylol- units glycol hexanediol propane glycol propaneglycol propane Content 0.04 0.04 0.01 0.04 0.01 0.04 0.01 (% by mole)Polycarboxylic Type — — — — — acid monomer units Content — — — — — (% bymole) Total content of polycarboxylic acid 0.07 0.07 0.04 0.08 0.09monomer units including polyol monomer units and diglycolic acid monomerunits (% by mole) Degree of discoloration of copolymer 29 33 34 33 39Results Degree of discoloration after the meld heat 39 43 44 44 48 ofstability test evaluation Oxygen gas permeability of a melt-shaped 8.38.2 8.3 8.6 8.7 sheet (cc/m² · day · atm) Strength of the melt-shapedsheet 5 or more 5 or more 5 or more 5 or more 5 or more Biodegradabilityof the melt-shaped Bio- Bio- Bio- Biodegradable Biodegradable sheet insoil degradable degradable degradableNote:“—” means “not detected”.

TABLE 4 Example Comparative Example 11 Example 12 Example 13 Example 1415 Example 5 Results Weight average molecular weight (Mw) 186,000185,000 189,000 280,000 189,000 165,000 of Content of glycolic acidmonomer 88.96 88.96 88.63 88.62 88.25 93.95 the unit (% by mole)analysis Non-glycolic, Type Lactic Lactic Lactic Lactic acid LacticLactic of the hydroxycarboxylic acid acid acid acid acid obtained acidmonomer Content 10.96 10.96 9.57 9.56 7.93 4.21 copolymer units (% bymole) Average chain 1.01 1.01 1.05 1.01 1.05 1.02 length Content ofdiglycolic acid monomer 0.04 0.03 0.03 0.03 0.03 0.03 unit (% by mole)Polyol monomer Type Neopentyl Neopentyl Neopentyl Neopentyl Trimethylol-Neopentyl Neopentyl units glycol glycol glycol glycol propane glycolglycol Content 0.04 0.04 0.90 0.90 0.01 1.91 0.92 (% by mole)Polycarboxylic Type — Oxalic Adipic Adipic acid Adipic Adipic acidmonomer acid acid acid acid units Content — 0.01 0.87 0.88 1.88 0.89 (%by mole) Total content of Polycarboxylic acid 0.08 0.08 1.80 1.82 3.821.84 monomer units including, polyol monomer units and diglycolic acidmonomer units (% by mole) Degree of discoloration of copolymer 29 28 3033 30 34 Results Degree of discoloration after the 40 39 39 42 38 110 ofmeld heat stability test evaluation Oxygen gas permeability of a 8.5 8.58.8 9.2 12.0 8.3 melt-shaped sheet (cc/m² · day · atm) Strength of themelt-shaped sheet 5 or more 5 or more 5 or more 5 or more 5 or more 5 ormore Biodegradability of the melt-shaped Bio- Bio- Bio- BiodegradableBio- Bio- sheet in soil degradable degradable degradable degradabledegradableNote:“—” means “not detected”.

TABLE 5 Example 16 Example 17 Example 18 Example 19 Example 20 Resultsof Weight average molecular weight (Mw) 178,000 148,000 132,000 152,00093,000 the Content of glycolic acid monomer unit (% by mole) 88.98 88.9388.91 88.92 88.98 analysis Non-glycolic, Type Lactic acid Lactic acidLactic acid Lactic acid Lactic acid of the hydroxycarboxylic acidContent (% by mole) 11.00 11.01 11.01 11.01 11.00 obtained monomer unitsAverage chain length 1.02 1.05 1.02 1.02 1.02 copolymer Content ofdiglycolic acid monomer unit (% by mole) 0.02 0.06 0.08 0.07 0.02 Polyolmonomer units Type — — — — — Content (% by mole) — — — — —Polycarboxylic acid Type — — — — — monomer units Content (% by mole) — —— — — Total content of polycarboxylic acid monomer units 0.02 0.06 0.080.07 0.02 including polyol monomer units and diglycolic acid monomerunits (% by mole) Degree of discoloration of copolymer 28 28 28 28 27Results of Degree of discoloration after the meld heat 39 44 48 46 38evaluation stability test Oxygen gas permeability of a melt-shaped sheet8.1 8.1 8.0 8.0 8.1 (cc/m² · day · atm) Strength of the melt-shapedsheet 5 or more 5 or more 5 or more 5 or more 4 Biodegradability of themelt-shaped sheet in Biodegradable Biodegradable BiodegradableBiodegradable Biodegradable soilNote:“—” means “not detected”.

TABLE 6 Comparative Comparative Comparative Comparative ComparativeComparative Example 6 Example 7 Example 8 Example 9 Example 10 Example11 Results of Weight average molecular weight (Mw) 186,000 179,000184,000 109,000 175,000 183,000 the Content of glycolic acid monomerunit (% by 88.59 88.58 88.62 88.84 94.00 83.00 analysis mole) of theNon-glycolic, Type Lactic acid Lactic acid Lactic acid Lactic acidLactic acid Lactic acid obtained hydroxycarboxylic acid Content (% bymole) 11.00 11.00 11.00 11.02 6.00 17.00 copolymer monomer units Averagechain 1.02 1.02 1.02 1.02 2.08 2.36 length Content of diglycolic acidmonomer unit (% by 0.20 0.21 0.18 0.14 — — mole) Polyol monomer unitsType Neopentyl Neopentyl Neopentyl — — — glycol glycol glycol Content (%by mole) 0.21 0.21 0.20 — — — Polycarboxylic acid Type — — — — — —monomer units Content (% by mole) — — — — — — Total content ofpolycarboxylic acid monomer 0.41 0.42 0.38 0.14 — — units includingpolyol monomer units and diglycolic acid monomer units (% by mole)Degree of discoloration of copolymer 40 39 37 38 30 29 Results of Degreeof discoloration after the meld heat 224 242 196 158 92 58 evaluationstability test Oxygen gas permeability of a melt-shaped sheet 8.7 8.88.8 8.3 8.8 28.0 (cc/m² · day · atm) Strength of the melt-shaped sheet 5or more 5 or more 5 or more 4 5 or more 5 or more Biodegradability ofthe melt-shaped sheet in Biodegradable Bio- Bio- Bio- Bio- Bio- soildegradable degradable degradable degradable degradableNote:“—” means “not detected”.

INDUSTRIAL APPLICABILITY

The glycolic acid copolymer of the present invention is a high quality,high molecular weight product which is advantageous not only in that thecopolymer enables production of a shaped article exhibiting excellentgas barrier property, satisfactory mechanical strength and satisfactorybiodegradability, but also in that the copolymer exhibits high heatstability, thereby greatly suppressing the occurrence of discolorationeven when melt-shaped at high temperatures. Further, by the method ofthe present invention, the above-mentioned glycolic acid copolymer canbe produced efficiently and stably.

1. A glycolic acid copolymer comprising: (a) 80 to less than 95% by moleof glycolic acid monomer units, (b) 5.0 to 20.0% by mole ofnon-glycolic, hydroxycarboxylic acid monomer units, and (c) 0 to 0.10%by mole of diglycolic acid monomer units, said non-glycolic,hydroxycarboxylic acid monomer units (b) constituting a plurality ofsegments each independently consisting of at least one non-glycolic,hydroxycarboxylic acid monomer unit (b), wherein said segments have anaverage chain length of from 1.00 to 1.50 in terms of the average numberof non-glycolic, hydroxycarboxylic acid monomer unit or units (b), thetotal of said components (a), (b) and (c) being 100% by mole, saidglycolic acid copolymer having a weight average molecular weight of50,000 or more.
 2. The glycolic acid copolymer according to claim 1,wherein the weight average molecular weight of said glycolic acidcopolymer is 80,000 or more.
 3. The glycolic acid copolymer according toclaim 1 or 2, wherein the amount of diglycolic acid monomer units (c) isfrom more than 0 to 0.09% by mole, based on the total molar amount ofcomponents (a), (b) and (c).
 4. The glycolic acid copolymer according toclaim 1 or 2, wherein the weight average molecular weight of saidglycolic acid copolymer is 100,000 or more.
 5. The glycolic acidcopolymer according to claim 1 or 2, wherein the average chain length ofsaid segments each independently consisting of at least onenon-glycolic, hydroxycarboxylic acid monomer unit (b) is from 1.00 to1.20.
 6. The glycolic acid copolymer according to claim 1 or 2, whereinsaid non-glycolic, hydroxycarboxylic acid monomer units (b) arenon-glycolic, monohydroxymonocarboxylic acid monomer units.
 7. Theglycolic acid copolymer according to claim 1 or 2, which furthercomprises a polyol monomer unit (d).
 8. The glycolic acid copolymeraccording to claim 7, wherein said polyol monomer unit (d) comprises atleast one member selected from the group consisting of monomer unitsderived from a diol having 3 or more carbon atoms and monomer unitsderived from a compound having 4 or more carbon atoms and 3 or morehydroxyl groups in the molecule.
 9. The glycolic acid copolymeraccording to claim 8, wherein said polyol monomer unit (d) comprises amonomer unit derived from a polyol having 5 or more carbon atoms and 2or 3 hydroxyl groups in the molecule.
 10. The glycolic acid copolymeraccording to claim 9, wherein said polyol monomer units (d) areneopentyl glycol monomer units.
 11. The glycolic acid copolymeraccording to of claim 7, which further comprises a polycarboxylic acidmonomer unit (e) other than diglycolic acid monomer units, wherein thetotal amount of the polyol monomer units (d), the polycarboxylic acidmonomer units (e), and the diglycolic acid monomer units (c) is lessthan 2.0% by mole, based on the total molar amount of components (a),(b), (c), (d) and (e).
 12. The glycolic acid copolymer according toclaim 11, wherein the total amount of the polyol monomer units (d), thepolycarboxylic acid monomer units (e), and the diglycolic acid monomerunits (c) is from more than 0.02 to less than 2.0% by mole, based on thetotal molar amount of components (a), (b), (c), (d) and (e), and theamount of the polyol monomer units (d) is from 0.02 to less than 2.0% bymole, based on the total molar amount of components (a), (b), (c), (d)and (e).
 13. The glycolic acid copolymer according to claim 1 or 2,wherein said non-glycolic, hydroxycarboxylic acid monomer units (b)comprise at least one member selected from the group consisting oflactic acid monomer units and 6-hydroxyhexanoic acid monomer units. 14.The glycolic acid copolymer according to claim 1 or 2, which is obtainedby polycondensing at least one starting material selected from the groupconsisting of glycolic acid and a derivative thereof with a reactantcopolymerizable with said at least one starting material, wherein saidreactant comprises at least one member selected from the groupconsisting of a non-glycolic, hydroxycarboxylic acid and a derivativethereof.
 15. A method for producing a glycolic acid copolymer, whichcomprises the steps of: (A) providing a raw material mixture comprisingat least one starting material selected from the group consisting ofglycolic acid and a derivative thereof, and a reactant copolymerizablewith said at least one starting material, wherein said reactantcomprises at least one member selected from the group consisting of anon-glycolic, hydroxycarboxylic acid, a derivative thereof andoptionally at least one compound selected from the group consisting of apolyol, a polycarboxylic acid and a derivative of the polycarboxylicacid, and subjecting said raw material mixture to a preliminarypolycondensation reaction at a temperature in the range of from 20 to160° C., thereby obtaining a reaction mixture containing a glycolic acidcopolymer prepolymer having a weight average molecular weight of from700 to 5,000, (B) elevating the temperature of the reaction mixture to190° C. within a period of 100 minutes as measured from the start of thetemperature elevation in step (B), and (C) performing a heat treatmentof said reaction mixture at a temperature in the range of from 190 to300° C. to effect a final polycondensation reaction, wherein said finalpolycondensation reaction is performed so as to obtain a glycolic acidcopolymer having a weight average molecular weight of 10,000 or more,wherein said final polycondensation reaction is performed underconditions wherein the increasing rate of weight average molecularweight of the glycolic acid copolymer being produced is maintained at1,000 per hour or more until the weight average molecular weight reachesat least 10,000.
 16. The method according to claim 15, wherein said heattreatment for effecting the final polycondensation reaction is performedso as to obtain the glycolic acid copolymer of claim 1 or 2, which has aweight average molecular weight of 50,000 or more.
 17. The methodaccording to claim 15, wherein said raw material mixture satisfies thefollowing formulae (1) to (3):0.8≦X¹≦0.95  (1),0.05≦X²  (2), andX¹ +X ² +X ³ +X ⁴=1  (3) wherein: X¹ represents the calculated molarratio of said at least one starting material selected from the groupconsisting of glycolic acid and a derivative thereof, X² represents thecalculated molar ratio of said at least one member selected from thegroup consisting of a non-glycolic, hydroxycarboxylic acid and aderivative thereof, X³ represents the calculated molar ratio of anoptional polyol, X⁴ represents the calculated molar ratio of at leastone optional raw material selected from the group consisting of apolycarboxylic acid and a derivative thereof, said calculated molarratio of each raw material being defined as the ratio of the molaramount of the unit structure obtained by hydrolysis of each raw materialto the total molar amount of the unit structures of all raw materials,and each of X³ and X⁴ is independently 0 or more.
 18. The methodaccording to claim 17, wherein said raw material mixture satisfies thefollowing formulae (4) and (5): $\begin{matrix}{{\frac{X^{4}}{X^{1} + X^{2}} \leq 0.001},{and}} & (4) \\{{0 < \frac{X^{3}}{X^{1} + X^{2}} \leq 0.01},} & (5)\end{matrix}$ wherein X¹ to X⁴ are as defined for formulae (1) to (3)above, provided that X³ is more than 0, and X⁴ is 0 or more.
 19. Themethod according to claim 17, wherein said raw material mixturesatisfies the following formulae (6) and (7): $\begin{matrix}{{0.001 < \frac{X^{4}}{X^{1} + X^{2}} \leq 0.088},{and}} & (6) \\{{1 \leq \frac{X^{3}}{X^{4}} \leq 2},} & (7)\end{matrix}$ wherein X¹ to X⁴ are as defined for formulae (1) to (3)above, provided that each of X³ and X⁴ is more than
 0. 20. The methodaccording to claim 17, wherein said raw material mixture satisfies thefollowing formula (8): $\begin{matrix}{{0.0002 \leq \frac{X^{3} + X^{4}}{X^{1} + X^{2} + X^{3} + X^{4}} < 0.02},} & (8)\end{matrix}$ wherein X¹ to X⁴ are as defined for formulae (1) to (3)above, provided that X³ is more than 0, and X⁴ is 0 or more.
 21. Amethod for producing a glycolic acid copolymer of claim 1 or 2, whichcomprises the steps of: crystallizing the glycolic acid copolymerobtained by the method of claim 15, thereby obtaining a crystallizedglycolic acid copolymer, and subjecting the obtained crystallizedglycolic acid copolymer to a solid phase polymerization, therebyincreasing the degree of polymerization of the crystallized glycolicacid copolymer.
 22. The method according to claim 21, wherein saidcrystallized glycolic acid copolymer before the solid phasepolymerization has a weight average molecular weight of 25,000 or more,as measured by gel permeation chromatography using, as an eluent, an 80mM sodium trifluoroacetate solution in hexafluoroisopropanol and using acalibration curve obtained with respect to standard monodispersepolymethyl methacrylate samples.
 23. A shaped article obtained from theglycolic acid copolymer of claim 1 to 1 or 2.